feat(tui): m move-to-project picker (§8.1)

`m` opens a list-pick overlay on the highlighted task — "(Unfile)" then
every project — and re-files it via `task.set_project` (cursor starts on
the task's current project). j/k navigate, Enter applies, Esc cancels.
Adds `Backend::set_project`, a `Mode::MoveToProject` overlay, and its
render. Navigation tests cover refile + cancel.

Closes the last Todoist-parity capture gap (§14 item 1).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/reference/tech-spec.md

@@ -254,12 +254,12 @@ Replaces obsidian.nvim. Telescope-backed. **Primarily the context / knowledge-ba
 
 - **Crate `crates/heph-tui`** ✅ — `ratatui` (which re-exports `crossterm`), a **thin client of the daemon unix socket** (reuse `hephd::Client`); never touches SQLite, same as nvim. `App` is generic over a `Backend` seam so navigation/triage logic is unit-testable without a terminal or daemon; `ui::render` is pure.
 - **Layout** ✅ — three panes: **sidebar** (the five §8.2 filter views + projects) · **task list** (attention-colored rows with compact human do/late) · **preview** (canonical-context doc body + `log.tail`).
-- **Gestures** ✅ — `j/k` move · `Tab`/`h`/`l` focus · `a` **single-line NL quick-add** (Todoist-style: `Buy milk tomorrow p2 #Work every week` → title + attention `p1`..`p4` + do-date + `every …` recurrence + `#project`; no `#project` files it under the selected one) · `x` done · `s` skip · `A` cycle attention · `e` reschedule do-date · `b` push-to-blue · `d` drop · `D` **delete/tombstone** (y/N confirm — true soft-delete, recurring included) · `o` edit context in nvim · `/` **FTS search** (overlay; Enter opens a hit — a task at its context doc — in nvim) · `r` refresh · `q` quit. The sidebar lists the **§8.2 named filter views** — [[design]] §6.2 "filters = saved views" made interactive. Recurring tasks show a **`↻` marker**, and the **selected row expands inline** with a dimmed detail block (project · recurrence rule · do/late). *(Remaining: move-to-project — needs a new `task.set_project` RPC, no link-remove RPC yet; humanizing the displayed RRULE is later polish.)*
+- **Gestures** ✅ — `j/k` move · `Tab`/`h`/`l` focus · `a` **single-line NL quick-add** (Todoist-style: `Buy milk tomorrow p2 #Work every week` → title + attention `p1`..`p4` + do-date + `every …` recurrence + `#project`; no `#project` files it under the selected one) · `x` done · `s` skip · `A` cycle attention · `e` reschedule do-date · `b` push-to-blue · `d` drop · `D` **delete/tombstone** (y/N confirm — true soft-delete, recurring included) · `m` **move-to-project** (a list-pick overlay — "(Unfile)" then every project; backed by `task.set_project`) · `o` edit context in nvim · `/` **FTS search** (overlay; Enter opens a hit — a task at its context doc — in nvim) · `r` refresh · `q` quit. The sidebar lists the **§8.2 named filter views** — [[design]] §6.2 "filters = saved views" made interactive. Recurring tasks show a **`↻` marker**, and the **selected row expands inline** with a dimmed detail block (project · recurrence rule · do/late). *(Remaining: humanizing the displayed RRULE is later polish.)*
 - **TUI ↔ nvim handoff** ✅ — `o` suspends the alternate screen and launches `nvim +"lua require('heph.node').open('<ctx-id>')"` (heph.nvim's live buffer surface), passing `$HEPH_SOCKET` so the child points at the same daemon, then restores and reloads. *(A nvim command shelling back to the TUI is later polish.)*
 - **Testing** ✅ — TDD against a real daemon; headless render assertions via `ratatui`'s `TestBackend`, plus in-memory navigation/input-flow units against a fake backend.
 - **Prereqs** (landed): **§8.2 filter views**; the CLI-complete task surface and `task.set_schedule`.
-- **Planned UX wave** (§14 roadmap, 2026-06-03) — all client-side over the existing `RankedTask` rows except move-to-project:
-  - **`m` move-to-project** — re-file the selected task via the new `task.set_project` RPC (the last Todoist-parity gap).
+- **`m` move-to-project** ✅ — re-file the selected task via the `task.set_project` RPC (a list-pick overlay), closing the last Todoist-parity gap.
+- **Planned UX wave** (§14 roadmap, 2026-06-03) — all client-side over the existing `RankedTask` rows:
   - **flag column + project-colored bullets** — a leading **flag glyph** colored by attention (red/orange/blue; **blank for white**, freeing the bullet for project identity); the **bullet `●` colored by its project** from a stable `hash(project_id) → hue` (HSL→truecolor, 256-color fallback; overlap acceptable; the glyph *shape* is reserved for future semantics). A stored, editable per-project color override is a later refinement.
   - **sort toggle `s`** — **default**: attention (red→orange→white→blue) → days-overdue (desc; no-date = 0) → project name → `created_at` (FIFO); **project mode**: project primary with **non-selectable `──── Name ────` separators** (`j`/`k` skip them). The view filter always runs before the sort.
   - **scrollbar** — a `ratatui` `Scrollbar` on the task list when it overflows.
@@ -446,7 +446,7 @@ See [[design]] §5–§7 for the constraints later phases impose on present choi
 >
 > The remaining work is the **UX roadmap agreed 2026-06-03** (design conversation with the owner). It is documented docs-first — the bigger items have design sections above (`heph-tui` UX in §8.1, frontmatter in §8.3, wiki-links-by-id in §8.4) — and built in this order:
 
-1. ⏳ **`heph-tui` — move-to-project (§8.1) — last Todoist-parity gap:** NL quick-add and `/` FTS search are **done**; re-filing a task's project needs a new **`task.set_project` RPC** (tombstone the old `in-project` link + add the new — there's no link-remove RPC today; OR-set link semantics, no task-scalar op). Small backend slice + a TUI gesture (`m`). Also **unblocks** the project-edit path of the frontmatter surface (§8.3).
+1. ✅ **`heph-tui` — move-to-project (§8.1) — DONE:** the **`task.set_project` RPC** (tombstone the old `in-project` link + add the new — OR-set semantics, no task-scalar op; given project must be a live project-kind node) plus the TUI `m` list-pick overlay and `heph edit --project <name>|none` (which also fixed a duplicate-link bug in the old re-file path). Unblocks the project-edit path of the frontmatter surface (§8.3).
 2. ⏳ **`heph-tui` task-list UX wave (§8.1) — no backend (`RankedTask` already carries every field):**
    - **(a) flag column + project-colored bullets** — a leading **flag glyph** colored by attention (red/orange/blue; **blank for white**), and the **bullet `●` colored by its project** via a stable `hash(project_id) → hue` (HSL→truecolor `Color::Rgb`, 256-color fallback). Hashing is chosen for stability-under-insertion over golden-angle spread; overlap is acceptable. The bullet **glyph shape** is reserved for future semantics. A per-project **color override** (stored on the project node, editable) is a later refinement — colors are derived client-side for now (no schema change).
    - **(b) sort toggle `s`** — **default**: attention (red→orange→white→blue) → days-overdue (descending; no-date = 0) → project (name) → `created_at` (FIFO). **project mode**: project is primary, with **non-selectable `──── Name ────` separator rows** between groups (`j`/`k` skip them). View filtering always runs **before** the sort.