feat: productivity suite — task loop, workflow, theming, docs & more (#197)

## Summary

A large productivity-focused feature branch delivering a suite of improvements across automation, project management, theming, performance, and documentation.

### Features

- **Guided Project Workflow** (#189) — Four-phase workflow panel (Discuss → Plan → Execute → Verify) to keep projects structured from idea to completion
- **Automated Task Loop** (#179) — Per-task conversation orchestration with wave-based parallel execution, blocked-task detection, and concurrency control
- **Wave-Based Parallel Execution** (#191) — Tasks run in dependency-aware waves with configurable concurrency; independent tasks execute in parallel
- **Auto-Commit After Task Completion** (#192) — Task Loop optionally commits after each completed task so progress is never lost
- **PRD Creator** (#180) — AI-assisted PRD and task list panel that outputs `hikari-tasks.json` for the Task Loop to consume
- **Project Context Panel** (#188) — Persistent `PROJECT.md`, `REQUIREMENTS.md`, `ROADMAP.md`, and `STATE.md` files injected into Claude's context automatically
- **Codebase Mapper** (#190) — Generates a `CODEBASE.md` architectural summary so Claude always understands the project structure
- **Community Preset Themes** (#181) — Six built-in community themes: Dracula, Catppuccin Mocha, Nord, Solarized Dark, Gruvbox Dark, and Rosé Pine
- **In-App Changelog Panel** (#193) — Fetches release notes from GitHub at runtime and displays them inside the app
- **Full Embedded Documentation** (#196) — Replaced the single-page help modal with a 12-page paginated docs browser featuring a sidebar TOC, prev/next navigation, keyboard navigation (arrow keys, `?` shortcut), and comprehensive coverage of every feature

### Performance & Fixes

- **Lazy Loading & Virtualisation** (#194) — Virtual windowing for conversation history, markdown memoisation, and debounced search for smooth rendering of large sessions
- **Ctrl+C Copy Fix** (#195) — `Ctrl+C` now copies selected text as expected; interrupt-Claude behaviour only fires when no text is selected

### UX

- Back-to-workflow button in PRD Creator and Task Loop panels for easy navigation
- Navigation icon cluster replaced with a single clean dropdown menu

## Closes

Closes #179
Closes #180
Closes #181
Closes #188
Closes #189
Closes #190
Closes #191
Closes #192
Closes #193
Closes #194
Closes #195
Closes #196

---

✨ This PR was created with help from Hikari~ 🌸

Reviewed-on: #197
Co-authored-by: Hikari <hikari@nhcarrigan.com>
Co-committed-by: Hikari <hikari@nhcarrigan.com>

src/lib/components/Markdown.svelte

@@ -108,15 +108,19 @@
     return processed;
   }
 
-  function renderMarkdown(text: string): string {
+  // Two-stage reactive rendering:
+  // Stage 1 — only re-runs when `content` changes (expensive: marked + hljs + spoilers)
+  let parsedHtml = $derived.by(() => {
     try {
-      const html = marked.parse(text) as string;
-      const withSpoilers = processSpoilers(html);
-      return highlightSearchMatches(withSpoilers, searchQuery);
+      const html = marked.parse(content) as string;
+      return processSpoilers(html);
     } catch {
-      return text;
+      return content;
     }
-  }
+  });
+
+  // Stage 2 — re-runs when search changes; skips re-parsing markdown entirely
+  let renderedHtml = $derived(highlightSearchMatches(parsedHtml, searchQuery));
 
   function handleSpoilerClick(event: Event) {
     const target = event.target as HTMLElement;
@@ -191,7 +195,7 @@
   role="presentation"
 >
   <!-- eslint-disable-next-line svelte/no-at-html-tags -- Markdown rendering requires @html; content is from Claude API -->
-  {@html renderMarkdown(content)}
+  {@html renderedHtml}
 </div>
 
 <style>