skeleton: plugin layout + docs, skill/agent migration deferred to iter 1

Establishes the repository structure for the skills plugin:
- README + INSTALL describing the two-layer split (plugin
  mechanics vs per-project profile)
- docs/design, profile-schema, pipeline, agent-template covering
  the universal discipline constants and the profile slot model
- templates/project-profile.yml as a copy-and-fill starting point
- templates/CLAUDE.md.fragment with the baseline orchestrator
  rules a project can import
- install.sh / uninstall.sh wiring skills/ + agents/ into
  ~/.claude/ via idempotent symlinks
- skills/ and agents/ directories empty except for migration
  READMEs; the actual SKILL bodies and agent files migrate
  from ~/dev/ailang/skills/ in the next iteration.

No skill or agent runs yet — this commit only stands up the
structure and documents the substitution model.

agents/README.md

@@ -0,0 +1,54 @@
+# agents/
+
+One subdirectory per skill, mirroring the `skills/` layout.
+Each holds the agent files that the corresponding skill
+dispatches.
+
+The skeleton commit ships this directory empty. Agent files
+are migrated from AILang's in-tree
+`~/dev/ailang/skills/<skill>/agents/` and generalised against
+the agent template (`../docs/agent-template.md`) and the
+profile schema (`../docs/profile-schema.md`) in **iteration 1**.
+
+Expected layout after migration:
+
+```
+agents/
+├── brainstorm/
+│   └── grounding-check.md
+├── planner/
+│   └── plan-recon.md
+├── implement/
+│   ├── implement-orchestrator.md
+│   ├── implementer.md
+│   ├── spec-reviewer.md
+│   ├── quality-reviewer.md
+│   └── tester.md
+├── audit/
+│   ├── architect.md
+│   └── bencher.md
+├── debug/
+│   └── debugger.md
+├── fieldtest/
+│   └── fieldtester.md
+└── docwriter/
+    └── docwriter.md
+```
+
+Migration checklist per agent:
+
+1. Drop the `ailang-` prefix from the `name:` frontmatter
+   field. The agent path is the disambiguator.
+2. Replace hardcoded standing-reading paths
+   (`design/INDEX.md`, etc.) with a reference to the profile's
+   `standing_reading` section.
+3. Replace project-specific Iron Law clauses with the universal
+   discipline constants; project-specific clauses go to the
+   project's own `CLAUDE.md`.
+4. Verify the body still reads coherently for a generic project
+   (see the skills/ migration checklist).
+5. Confirm the `tools:` frontmatter list matches the agent
+   template's role-based conventions (read-only review vs
+   implementation vs orchestrator).
+6. Confirm the agent does **not** have `Agent` in its tools list
+   (no nested subagent dispatch).