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

[tusharmagar]

…lude directive

Skills move out of packages/core/src/application/assistant/skills/*/skill.ts (TS string constants) into apps/skills//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:}} 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.