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.

crates/storage/src/migrations.rs

@@ -377,6 +377,29 @@ const MIGRATIONS: &[(i64, &str, &str)] = &[
             ON feedback(profile_id, target_type, created_at DESC);
         "#,
     ),
+    (
+        11,
+        "tasks: energy tagging for match-my-energy sort",
+        r#"
+        -- Phase 3 of the feature-complete roadmap: replaces the cut
+        -- temptation-bundling feature with a deterministic client-side
+        -- sort that matches tasks to the user's current energy state.
+        -- NULL is the expected normal case — users who never tag get
+        -- Medium-equivalent treatment at sort time (see Match-my-energy
+        -- logic in src/lib/pages/TasksPage.svelte).
+        --
+        -- profile_id is deliberately absent from the index: tasks
+        -- currently carry no profile_id column, so a per-profile index
+        -- is out of scope until the broader task → profile migration
+        -- lands. See HANDOVER deferred list.
+        ALTER TABLE tasks
+            ADD COLUMN energy TEXT
+            CHECK (energy IS NULL OR energy IN ('high', 'medium', 'brain_dead'));
+
+        CREATE INDEX idx_tasks_energy_created
+            ON tasks(energy, created_at DESC);
+        "#,
+    ),
 ];
 
 /// Split SQL into individual statements, respecting BEGIN...END trigger blocks.
@@ -526,7 +549,7 @@ mod tests {
             .fetch_one(&pool)
             .await
             .unwrap();
-        assert_eq!(count, 10);
+        assert_eq!(count, 11);
 
         sqlx::query("INSERT INTO settings (key, value) VALUES ('test', 'value')")
             .execute(&pool)
@@ -545,7 +568,7 @@ mod tests {
             .fetch_one(&pool)
             .await
             .unwrap();
-        assert_eq!(count, 10);
+        assert_eq!(count, 11);
     }
 
     #[tokio::test]