feat(skills): single-source skill system with markdown SKILL.md + include directive

Skills move out of packages/core/src/application/assistant/skills/*/skill.ts
(TS string constants) into apps/skills/<id>/SKILL.md (Agent Skills spec format
— YAML frontmatter + markdown body). One directory, one loader, one place to
look at every skill the agent can load.

Key change vs the old dev system: a `{{include:<skill-id>}}` directive lets one
skill transclude another. This removes the parallel TS constant for the
knowledge-note style guide — it now lives at apps/skills/knowledge-note-style/
(hidden from catalog) and is pulled into doc-collab + the live-note and
background-task agents via the resolver instead of via a TS import.

Infrastructure:
- packages/core/src/skills/ — types, skill-md-parser, FS-backed official repo,
  SkillResolver with recursive {{include:<id>}} expansion + cycle detection
- packages/shared/src/skill.ts — SkillFrontmatter, SkillCatalogEntry,
  ResolvedSkill schemas
- DI: officialSkillsRepo + skillResolver registered; registerSkillsDir helper
  wires the path before any consumer resolves
- IPC: skills:list / skills:get (read-only) for the Settings UI
- Main: resolveSkillsDir picks Resources/skills (packaged) or repo apps/skills
  (dev). forge.config.cjs ships apps/skills/ as extraResource.

Consumer refactor:
- buildCopilotInstructions: catalog markdown built from resolver.getCatalog()
- builtin-tools: loadSkill uses resolver, new listSkills tool
- background-tasks/agent + live-note/agent: now async builders that load
  the knowledge-note-style skill content via resolver
- runtime.loadAgent: awaits the now-async builders
- Deleted: assistant/skills/ directory, knowledge-note-style.ts

UI:
- New SkillsSettings component (read-only list + detail view) wired into
  Settings dialog as the "Skills" tab.

apps/skills/app-navigation/SKILL.md

@@ -0,0 +1,86 @@
+---
+name: app-navigation
+description: >-
+  Navigate the app UI - open notes, switch views, filter/search the knowledge base, and manage saved views.
+metadata:
+  title: "App Navigation"
+---
+
+# App Navigation Skill
+
+You have access to the **app-navigation** tool which lets you control the Rowboat UI directly — opening notes, switching views, filtering the knowledge base, and creating saved views.
+
+## Actions
+
+### open-note
+Open a specific knowledge file in the editor pane.
+
+**When to use:** When the user asks to see, open, or view a specific note (e.g., "open John's note", "show me the Acme project page").
+
+**Parameters:**
+- ` + "`path`" + `: Full workspace-relative path (e.g., ` + "`knowledge/People/John Smith.md`" + `)
+
+**Tips:**
+- Use ` + "`workspace-grep`" + ` first to find the exact path if you're unsure of the filename.
+- Always pass the full ` + "`knowledge/...`" + ` path, not just the filename.
+
+### open-view
+Switch the UI to the graph or bases view.
+
+**When to use:** When the user asks to see the knowledge graph, view all notes, or open the bases/table view.
+
+**Parameters:**
+- ` + "`view`" + `: ` + "`\"graph\"`" + ` or ` + "`\"bases\"`" + `
+
+### update-base-view
+Change filters, columns, sort order, or search in the bases (table) view.
+
+**When to use:** When the user asks to find, filter, sort, or search notes. Examples: "show me all active customers", "filter by topic=hiring", "sort by name", "search for pricing".
+
+**Parameters:**
+- ` + "`filters`" + `: Object with ` + "`set`" + `, ` + "`add`" + `, ` + "`remove`" + `, or ` + "`clear`" + ` — each takes an array of ` + "`{ category, value }`" + ` pairs.
+  - ` + "`set`" + `: Replace ALL current filters with these.
+  - ` + "`add`" + `: Append filters without removing existing ones.
+  - ` + "`remove`" + `: Remove specific filters.
+  - ` + "`clear: true`" + `: Remove all filters.
+- ` + "`columns`" + `: Object with ` + "`set`" + `, ` + "`add`" + `, or ` + "`remove`" + ` — each takes an array of column names (frontmatter keys).
+- ` + "`sort`" + `: ` + "`{ field, dir }`" + ` where dir is ` + "`\"asc\"`" + ` or ` + "`\"desc\"`" + `.
+- ` + "`search`" + `: Free-text search string.
+
+**Tips:**
+- If unsure what categories/values are available, call ` + "`get-base-state`" + ` first.
+- For "show me X", prefer ` + "`filters.set`" + ` to start fresh rather than ` + "`filters.add`" + `.
+- Categories come from frontmatter keys (e.g., relationship, status, topic, type).
+- **CRITICAL: Do NOT pass ` + "`columns`" + ` unless the user explicitly asks to show/hide specific columns.** Omit the ` + "`columns`" + ` parameter entirely when only filtering, sorting, or searching. Passing ` + "`columns`" + ` will override the user's current column layout and can make the view appear empty.
+
+### get-base-state
+Retrieve information about what's in the knowledge base — available filter categories, values, and note count.
+
+**When to use:** When you need to know what properties exist before filtering, or when the user asks "what can I filter by?", "how many notes are there?", etc.
+
+**Parameters:**
+- ` + "`base_name`" + ` (optional): Name of a saved base to inspect.
+
+### create-base
+Save the current view configuration as a named base.
+
+**When to use:** When the user asks to save a filtered view, create a saved search, or says "save this as [name]".
+
+**Parameters:**
+- ` + "`name`" + `: Human-readable name for the base.
+
+## Workflow Example
+
+1. User: "Show me all people who are customers"
+2. First, check what properties are available:
+   ` + "`app-navigation({ action: \"get-base-state\" })`" + `
+3. Apply filters based on the available properties:
+   ` + "`app-navigation({ action: \"update-base-view\", filters: { set: [{ category: \"relationship\", value: \"customer\" }] } })`" + `
+4. If the user wants to save it:
+   ` + "`app-navigation({ action: \"create-base\", name: \"Customers\" })`" + `
+
+## Important Notes
+- The ` + "`update-base-view`" + ` action will automatically navigate to the bases view if the user isn't already there.
+- ` + "`open-note`" + ` validates that the file exists before navigating.
+- Filter categories and values come from frontmatter in knowledge files.
+- **Never send ` + "`columns`" + ` or ` + "`sort`" + ` with ` + "`update-base-view`" + ` unless the user specifically asks to change them.** Only pass the parameters you intend to change — omitted parameters are left untouched.