feat(core): task.set_project — move-to-project with OR-set link semantics (§8.1)

Add `Store::set_task_project` (heph-core + RemoteStore) and the
`task.set_project` RPC: tombstone the task's existing `in-project` link(s)
and add a new one (or none, to unfile). A given project id must name a
live project-kind node, else InvalidArg/NodeNotFound.

Route `heph edit --project` through it, fixing a duplicate-link bug (the
old path added an in-project link without removing the prior one);
`--project none` now unfiles. Factor a `links::tombstone` helper out of
`sync_wiki_links`.

Tests: core move/unfile/reject + a duplicate-link regression; a socket
dispatch test. The TUI `m` gesture follows in the next commit.

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

docs/changelog.d/v1-prototype.feature.md

@@ -23,4 +23,5 @@ Begin the v1 prototype (Phase 1, tech-spec §11.1), built in TDD slices:
 - CLI as a complete task surface (§1, §6.2.1): `heph` now implements the entire daemon API and is the task capture/scripting surface. Structured fields are flags with **human dates** (`--do-date tomorrow|+3d|fri|YYYY-MM-DD`, shown back compactly in `next`/`list`) and **recurrence** (`--recur` presets/natural-language like "every 3 days", or a raw `--rrule`). New verbs: `list`, `done`/`drop`/`skip`, `attention`, `edit` (reschedule do-date/late-on/recurrence, re-attention, re-file — backed by the new `task.set_schedule` RPC), `promote`, `show`, `log` (append or tail), `health`, `node update`/`rm`, `resolve`, `links`/`backlinks`, `link add`, `project add [--parent]`, `sync [--status]`, `conflicts [resolve]`. Projects are referenced by name. Date/recurrence parsing is unit-tested; the new verbs have real-socket process tests.
 - Daemon lifecycle is now an explicit OS service, and all surfaces are connect-only (no more auto-spawn). `heph daemon start/stop/restart/status/uninstall` idempotently manages a launchd agent (macOS) or systemd user service (Linux) that runs `hephd` on your default store; `heph.nvim` no longer spawns or supervises a daemon — it just connects and points you at `heph daemon start` if none is running. Rationale: once the CLI became a first-class surface, a daemon owned by one surface couldn't be shared (see [[run-the-daemon]], [[design]] §4).
 - Filter views (§8.2) — saved agenda slices, so the agenda isn't one flat list. `heph view <name>` runs a built-in view (`tom` Top of Mind, `ondeck` On Deck, `chores`, `work` Work Tasks, `tasks`) seeded from the owner's Todoist filter queries; `heph view` with no name lists them, and `:Heph view <name>` does the same in Neovim. Under the hood, `list` now takes a `ListFilter` predicate-as-data (attention include/exclude sets, project-subtree scope, project exclusions, an actionable do-date gate), and views resolve project names to ids and expand each to its `parent`-link subtree. The Schedule view is intentionally omitted (time-of-day isn't modeled on date-grained do-dates).
-- `heph-tui` (§8.1) — a terminal task agenda/triage UI, the primary surface for working a large task set (the §6.2.1 Todoist study showed triage, not single edits, dominates). A `ratatui` app, thin client of the daemon socket. Three panes: a sidebar of the five filter views + your projects, an attention-colored task list with compact human do/late dates, and a preview of the highlighted task's context doc + recent log. Triage from the keyboard: `a` add (guided title → attention → do-date, filed under the selected project), `x` done, `s` skip, `d` drop, `A` cycle attention, `b` push to On Deck, `e` reschedule the do-date; `o` opens the task's context doc in your nvim (live, via heph.nvim) and returns. `j/k` move, `Tab`/`h`/`l` switch panes, `r` refresh, `q` quit. Run it with `heph-tui` (honors `--socket` / `$HEPH_SOCKET`). `a` is a Todoist-style single-line quick-add: `Buy milk tomorrow p2 #Work every week` parses into title + attention (p1–p4) + do-date + recurrence + project (multi-word project names match greedily; an unresolved `#tag` just stays in the title). `/` runs a full-text search whose results overlay the task list; Enter opens a hit (a task at its context doc) in nvim. Re-filing a task to a different project is the one remaining capture gap.
+- `heph-tui` (§8.1) — a terminal task agenda/triage UI, the primary surface for working a large task set (the §6.2.1 Todoist study showed triage, not single edits, dominates). A `ratatui` app, thin client of the daemon socket. Three panes: a sidebar of the five filter views + your projects, an attention-colored task list with compact human do/late dates, and a preview of the highlighted task's context doc + recent log. Triage from the keyboard: `a` add (guided title → attention → do-date, filed under the selected project), `x` done, `s` skip, `d` drop, `A` cycle attention, `b` push to On Deck, `e` reschedule the do-date; `o` opens the task's context doc in your nvim (live, via heph.nvim) and returns. `j/k` move, `Tab`/`h`/`l` switch panes, `r` refresh, `q` quit. Run it with `heph-tui` (honors `--socket` / `$HEPH_SOCKET`). `a` is a Todoist-style single-line quick-add: `Buy milk tomorrow p2 #Work every week` parses into title + attention (p1–p4) + do-date + recurrence + project (multi-word project names match greedily; an unresolved `#tag` just stays in the title). `/` runs a full-text search whose results overlay the task list; Enter opens a hit (a task at its context doc) in nvim.
+- Move-to-project (§8.1): a new `task.set_project` RPC re-files a task under another project (or unfiles it) with OR-set link semantics — the old `in-project` link is tombstoned and a new one added, so a task is never filed under two projects at once. `heph edit <task> --project <name>` now routes through it (fixing a bug where re-filing piled on a duplicate link), and `--project none` unfiles the task.