feat(energy): Phase 3 — match-my-energy task sort + tri-state tag column

Closes Phase 3 of the 2026-04-23 feature-complete roadmap. Incorporates
the Codex plan-review fixes from this session: profile-free index, tri-
state update command, and de-prioritise-not-hide semantics.

Storage (kon-storage):
- Migration v11 adds `energy TEXT` to `tasks` with a CHECK constraint on
  `high | medium | brain_dead | NULL`. Index `(energy, created_at DESC)`
  — deliberately not per-profile because the tasks table carries no
  profile_id column yet (tracked as a separate gap in HANDOVER).
- `TaskRow.energy: Option<String>` plus `task_row_from` read.
- `insert_task` signature grows by one optional arg (`energy`). Allowed
  `too_many_arguments` with a rationale comment — the positional shape
  matches the column order and flipping to a params struct would have
  rippled through every caller for cosmetic benefit only.
- New `set_task_energy(pool, id, Option<&str>) -> TaskRow`. Lives as its
  own function because `update_task` uses COALESCE to let `None` mean
  "preserve" — which would make clearing the tag impossible.
- Two new tests: round-trip including explicit NULL clear, and CHECK
  constraint rejection of unknown values.
- Tests updated for the v10 → v11 version bump.

Tauri (src-tauri):
- `TaskDto.energy`. `CreateTaskRequest.energy` (optional). Inline
  validation against the allowed set before hitting the DB, so frontend
  bugs surface as friendly errors instead of CHECK-constraint failures.
- New `set_task_energy_cmd` command mirroring the storage tri-state API.

Frontend (svelte):
- `EnergyLevel` type added to `types/app.ts`. `TaskDto`, `TaskEntry`, and
  `TaskDraft` grow an `energy` field.
- `SettingsState.currentEnergy` (persisted) + `matchMyEnergy` (persisted
  toggle). Defaults: null + false — no surface change until user opts in.
- `setTaskEnergy(id, EnergyLevel | null)` action on the task store.
  Calls the dedicated Tauri command, updates local state, broadcasts to
  sibling windows.
- `EnergyChip.svelte` — new component. Cycles unset → High → Medium →
  Brain-Dead → unset on click. Colour tokens: accent / warning /
  text-tertiary (deliberately not danger-red for Brain-Dead — the brief
  is explicit that this state must not feel pathologised).
- Chip rendered on every task row in TasksPage and every row in
  WipTaskList. Hidden-until-hover when energy is unset so untagged rows
  stay calm; always visible once tagged because the colour is the signal.
- Tasks page header gains a "I feel" segmented control and a
  "Match my energy" toggle. When both are active, matching tasks sort
  to the top — unset tasks are treated as Medium-equivalent. Nothing is
  ever hidden; this is a de-prioritisation, not a filter.

Deferred / out of scope:
- LLM-driven surfacing (brief says "The AI surfaces...") — deterministic
  client-side sort is v1; LLM layer is a later phase.
- tasks.profile_id + per-profile energy sort — separate migration.

All green: cargo build + 251 tests + clippy -D warnings (0 warnings)
+ fmt + svelte-check (0/0) + npm run build.

src-tauri/src/lib.rs

@@ -284,6 +284,7 @@ pub fn run() {
             commands::tasks::complete_task_cmd,
             commands::tasks::delete_task_cmd,
             commands::tasks::uncomplete_task_cmd,
+            commands::tasks::set_task_energy_cmd,
             commands::tasks::decompose_and_store,
             commands::tasks::extract_tasks_from_transcript_cmd,
             commands::tasks::list_subtasks_cmd,