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/lib/components/EnergyChip.svelte

@@ -0,0 +1,106 @@
+<script lang="ts">
+  // Phase 3 — Energy tag chip. Cycles a task's energy level through
+  // the spec's four states: unset → High → Medium → Brain-Dead → unset.
+  //
+  // Visual discipline: when energy is unset, the chip renders at
+  // `group-hover` opacity only so untagged rows stay calm. Once set,
+  // the chip is always visible because the colour IS the signal for
+  // the match-my-energy sort.
+  //
+  // Colour choices borrow the existing design tokens:
+  //   High       → accent (warm, on-brand, attention-ready)
+  //   Medium     → warning (amber, unforced)
+  //   Brain-Dead → text-tertiary (low-energy grey, not danger red —
+  //                the brief is explicit that this state must not feel
+  //                pathologised)
+  //
+  // Callers pass the task's current energy and a setter. This component
+  // owns no state — the task store is the source of truth.
+
+  import type { EnergyLevel } from "$lib/types/app";
+  import { Zap } from "lucide-svelte";
+
+  let {
+    energy = null as EnergyLevel | null,
+    onSelect,
+    size = "sm",
+    reduceMotion = false,
+  }: {
+    energy: EnergyLevel | null;
+    onSelect: (next: EnergyLevel | null) => void;
+    size?: "sm" | "md";
+    reduceMotion?: boolean;
+  } = $props();
+
+  // Cycle order lives here so the chip is the single authority on what
+  // "next" means. Tap once to tag, tap again to move up, tap past
+  // Brain-Dead to clear. Keyboard-equivalent via the <button> element.
+  const CYCLE: (EnergyLevel | null)[] = [null, "high", "medium", "brain_dead"];
+
+  function next(): EnergyLevel | null {
+    const idx = CYCLE.indexOf(energy);
+    return CYCLE[(idx + 1) % CYCLE.length];
+  }
+
+  function labelFor(level: EnergyLevel | null): string {
+    switch (level) {
+      case "high": return "High";
+      case "medium": return "Medium";
+      case "brain_dead": return "Brain-Dead";
+      default: return "No energy set";
+    }
+  }
+
+  let tooltip = $derived(
+    energy === null
+      ? "Tag energy (click to set)"
+      : `Energy: ${labelFor(energy)} — click to change`
+  );
+
+  // Icon dimensions. `md` is the one used on the Tasks-page main rows;
+  // `sm` is for the compact WIP list rows and micro-step children.
+  let iconSize = $derived(size === "md" ? 13 : 10);
+  let chipSize = $derived(size === "md" ? "h-5" : "h-4");
+</script>
+
+<button
+  type="button"
+  class="energy-chip inline-flex items-center justify-center rounded-md border px-1 {chipSize} text-[10px] font-medium
+    {energy === null
+      ? 'opacity-0 group-hover:opacity-100 text-text-tertiary border-border-subtle hover:border-accent hover:text-text-secondary'
+      : ''}
+    {energy === 'high'
+      ? 'text-accent border-accent bg-accent/10'
+      : ''}
+    {energy === 'medium'
+      ? 'text-warning border-warning bg-warning/10'
+      : ''}
+    {energy === 'brain_dead'
+      ? 'text-text-tertiary border-border bg-hover'
+      : ''}"
+  onclick={() => onSelect(next())}
+  aria-label={tooltip}
+  title={tooltip}
+  data-energy={energy ?? 'unset'}
+  style={reduceMotion
+    ? ''
+    : 'transition: opacity var(--duration-ui), color var(--duration-ui), border-color var(--duration-ui), background-color var(--duration-ui)'}
+>
+  <Zap size={iconSize} aria-hidden="true" />
+  {#if energy !== null && size === "md"}
+    <span class="ml-1">{labelFor(energy)}</span>
+  {/if}
+</button>
+
+<style>
+  .energy-chip {
+    cursor: pointer;
+    line-height: 1;
+    font-family: var(--font-family-body);
+  }
+
+  .energy-chip:focus-visible {
+    outline: 2px solid var(--color-accent);
+    outline-offset: 1px;
+  }
+</style>