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/code-with-agents/SKILL.md

@@ -0,0 +1,94 @@
+---
+name: code-with-agents
+description: >-
+  Write code, build projects, create scripts, or fix bugs by delegating to Claude Code or Codex via acpx.
+metadata:
+  title: "Code with Agents"
+---
+
+# Code with Agents Skill
+
+Use this skill when the user asks you to write code, build a project, create scripts, fix bugs, or do any software development task that should be delegated to a coding agent (Claude Code or Codex).
+
+## Important: delegate ALL coding work
+
+Once the user has chosen to use Claude Code or Codex, you MUST delegate ALL code-related tasks to the coding agent. This includes:
+- Writing, editing, or refactoring code
+- Reading, summarizing, or explaining code
+- Debugging and fixing bugs
+- Running tests or build commands
+- Exploring project structure
+- Any other task that involves interacting with a codebase
+
+Do NOT attempt to do any of these yourself — no reading files, no running commands, no writing code. You are the coordinator; the coding agent does the work. Your job is to translate the user's request into a clear prompt and pass it to the agent.
+
+## Prerequisites
+
+The user must have one of the following installed on their machine:
+- **Claude Code** — https://claude.ai/code
+- **Codex** — https://codex.openai.com
+
+These are external tools that you cannot install for the user.
+
+## Workflow
+
+### Step 1: Gather requirements
+
+Before running anything, confirm the following with the user:
+
+1. **Working directory** — Ask which folder the code should be written in, unless the user has already specified it. Example: "Which folder should I work in?"
+2. **Agent choice** — Ask whether to use **Claude Code** or **Codex**. Mention that the chosen agent must already be installed on their machine.
+
+### Step 2: Confirm execution plan
+
+Once you know the folder and agent, tell the user:
+
+> I'll use [Claude Code / Codex] to [description of the task] in `[folder]`. Permission requests from the coding agent itself (file writes, command execution, etc.) will be automatically approved once it starts. Wait for the user's confirmation before you execute anything.
+
+### Step 3: Execute with acpx
+
+Use the `executeCommand` tool to run the coding agent via acpx. The command format is:
+
+**For Claude Code:**
+` + "`" + `
+npx acpx@latest --approve-all --cwd <folder> claude exec "<prompt>"
+` + "`" + `
+
+**For Codex:**
+` + "`" + `
+npx acpx@latest --approve-all --cwd <folder> codex exec "<prompt>"
+` + "`" + `
+
+### Critical: flag order
+
+The `--approve-all` and `--cwd` flags are global flags and MUST come before the agent name (`claude` or `codex`). This is the correct order:
+
+` + "`" + `
+npx acpx@latest [global flags] <agent> exec "<prompt>"
+` + "`" + `
+
+**Correct:**
+` + "`" + `
+npx acpx@latest --approve-all --cwd ~/projects/myapp claude exec "fix the bug"
+` + "`" + `
+
+**Wrong (will fail):**
+` + "`" + `
+npx acpx@latest claude --approve-all exec "fix the bug"
+` + "`" + `
+
+### Writing good prompts
+
+When constructing the prompt for the coding agent:
+- Be specific and detailed about what to build or fix
+- Include file names, function signatures, and expected behavior
+- Mention any constraints (language, framework, style)
+- If the user gave you a short request, expand it into a clear, actionable prompt for the agent
+
+### Step 4: Report results
+
+After the command finishes, look for the summary that the coding agent produced at the end of its output and pass that along to the user as-is. Do not rewrite or add to it. Only add your own explanation if the command failed or the exit code is non-zero.
+
+Do NOT use file reference blocks (e.g. ```file:path/to/file```) when mentioning code files — they may not open correctly. Just refer to file paths as plain text.
+
+- If the exit code is 5, it means permissions were denied — this should not happen with `--approve-all`, but if it does, let the user know