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.

README.md

@@ -0,0 +1,75 @@
+# skills
+
+A self-contained set of development-cycle skills and agents for
+Claude Code. Originally distilled from the AILang project's
+in-tree `skills/` directory and generalised so it can carry the
+same discipline across any project.
+
+The plugin is **mechanics**: pipeline shape, hard-gates, TDD,
+RED-first bug fixing, agent-template, working-tree-as-quarantine,
+status protocol. It does **not** know your project's paths,
+build commands, vocabulary, or domain-specific contracts. Those
+live in a small per-project profile file
+(`.claude/dev-cycle-profile.yml`) plus the project's `CLAUDE.md`.
+
+## What's in the box
+
+Seven skills, each with the agents it primarily dispatches:
+
+| Skill | Trigger | Output | Mandatory? |
+|-------|---------|--------|------------|
+| `brainstorm` | New cycle starting | spec under the configured spec dir | Hard-gate before plan |
+| `planner` | New iteration within an open cycle | plan under the configured plan dir | Hard-gate before implement |
+| `implement` | Plan exists | code + tests, uncommitted in working tree | Standard iteration path |
+| `audit` | Cycle closing OR baseline drift suspected | drift report + regression report | Mandatory at cycle close |
+| `debug` | Bug observed | RED test in working tree + cause analysis | Mandatory RED-first for any bug |
+| `fieldtest` | Orchestrator-dispatched post-audit, surface-touching cycle | example fixtures + friction spec | Optional |
+| `docwriter` | API surface stable across N cycles | rustdoc / docstring sweep | Optional |
+
+Vocabulary is configurable. AILang calls a cycle a *milestone*
+and a sub-cycle an *iteration*; your project may call them
+*release* and *sprint*, or *epic* and *story*, or whatever fits.
+
+## The two-layer split
+
+This repo (the **plugin**) carries everything that is universal:
+
+- Pipeline form: `design → plan → execute → review → close`
+- Hard-gates between phases
+- TDD as an independent inner-loop discipline
+- RED-first bug fixes
+- Agent template (frontmatter / Iron Law / standing reading /
+  process / status / output / rationalisations / red flags)
+- Status protocol: `DONE / DONE_WITH_CONCERNS / PARTIAL / BLOCKED
+  / NEEDS_CONTEXT`
+- Working-tree-as-quarantine and only-orchestrator-commits
+- main HEAD sacrosanct
+- No nested subagent dispatch (Claude Code platform constraint)
+- No orphan agents
+
+Your project carries a small **profile** that fills the slots:
+
+- Paths: spec dir, plan dir, design ledger, code roots, bench dir
+- Commands: build, test, lint, regression scripts
+- Vocabulary: cycle name, sub-cycle name, ledger-entry name
+- Naming: counter prefix vs date prefix vs flat, slug shape
+- Standing reading list: concrete files, per role
+- Git: issue tracker kind, close marker, main-protection policy
+- Pipeline customisations: which phases are mandatory, when
+  optional ones fire
+
+See `docs/profile-schema.md` for the full schema and
+`templates/project-profile.yml` for a copy-and-fill starting point.
+
+## Install
+
+See `INSTALL.md`. In short: clone, run `install.sh`, then drop
+a `dev-cycle-profile.yml` into each project that should use the
+plugin.
+
+## Status
+
+This is the skeleton commit. The skill bodies and agent files
+still need to be migrated from AILang's in-tree
+`~/dev/ailang/skills/` and generalised against this plugin's
+profile schema. That migration is iteration 1.