Planning debug panel, todo auto-populate, scratchpad/persona improvements ...

- Planning debug panel: new Planning tab in debug/index.html shows raw
  phase 1/2 outputs and token counts per planning run, stored in
  session.planning_logs (new column in both SQLite and PostgreSQL)
- New GET /sessions/{id}/planning API endpoint
- PlanningDebugData internal event wires _run_planning() output into
  session storage; never forwarded to WebSocket clients
- Phase 3 (plan critic) disabled — to be reworked with reflect integration
- Todo tool: auto-populated from plan steps after phase 2; model only
  needs to call update/view, not set
- Scratchpad: clarified description and persona instructions; removed
  context_transfer from user-facing docs (internal mechanism only)
- web_search: switched to ddgs package, SearXNG as primary backend,
  DDG html-only fallback; added find_up action to filesystem tool
- Persona: added SCRATCHPAD and TODO sections with clear usage rules;
  added NAVI.md project context instructions
- chat.js: fixed subagent planning event fallthrough into parent UI;
  statusLabel cleared on first stream delta

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Add Prompts and Tools tabs to debug page ...

Backend:
- GET /agents/prompts — returns full built system prompt for every
  profile, broken into sections (persona / profile / profiles block)
  with char/token counts; mirrors Agent._build_system_prompt() exactly
- GET /agents/tools — now includes parameters schema alongside name
  and description

Debug page:
- Tab bar: Context / Prompts / Tools
- Prompts tab: profile sidebar + collapsible sections per prompt part
  (persona, profile prompt, profiles block), togglable tools list
- Tools tab: searchable list of all tools with description and
  parameter table (name, type, description, required marker)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Add standalone debug page at /debug ...

Replaces the old_webclient/debug.html with a proper self-contained
tool at debug/index.html. New features over the old page:
- Sidebar session list with profile, message count, pin indicator
- Auto-refresh toggle (3s interval)
- Refresh button
- Renders thinking blocks, is_plan and is_summary tags
- Shows tool call name on tool result messages
- Clickable image thumbnails (open full-size)
- All new fields from the current LLM context API

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>