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.

docs/design.md

@@ -0,0 +1,120 @@
+# Design
+
+## Why split plugin from profile
+
+The skills system originally evolved inside the AILang project,
+where it grew organically against AILang's specific paths,
+build commands, vocabulary, and contracts. Lifting it into a
+plugin requires a clean separation between what is universal
+(belongs in the plugin) and what is project-specific (belongs
+in a per-project profile).
+
+The litmus test: would a sentence in a SKILL or agent body
+still make sense in a Python web project, a Rust CLI, and a
+TypeScript library? If yes, plugin. If it mentions `cargo`,
+`crates/`, `design/INDEX.md`, `Form A`, or any project-specific
+identifier, it goes to the profile (as a slot) or to the
+project's `CLAUDE.md` (as sittenkodex).
+
+## Plugin layer (universal)
+
+The plugin owns:
+
+- **Pipeline form** — the directed graph of phases:
+  `design → plan → execute → review → close`, with the
+  bug-driven side path `debug → execute (mini)`.
+- **Hard-gates** — spec before plan, plan before implement,
+  audit before cycle-close. Skipping rules are codified per
+  skill.
+- **Agent template** — every agent file follows the same
+  structure: frontmatter (name, description, tools), Iron Law,
+  standing reading list, numbered process, status protocol,
+  output format, common rationalisations, red flags.
+- **TDD as an independent inner-loop discipline** — the
+  implementer agent carries TDD even when the plan task forgot
+  to script a RED-first step.
+- **RED-first bug fixes** — non-negotiable for any observable
+  misbehaviour; the debug skill is the gate.
+- **Status protocol** — `DONE / DONE_WITH_CONCERNS / PARTIAL /
+  BLOCKED / NEEDS_CONTEXT`, plus reviewer-specific terminal
+  states.
+- **Working-tree-as-quarantine** — agents write artefacts to
+  the working tree, never commit. Only the orchestrator commits.
+- **main HEAD sacrosanct** — no reset, no revert, by any actor.
+  main moves forward only via orchestrator commits.
+- **No nested subagent dispatch** — a hard Claude Code
+  platform constraint; the implement-orchestrator runs phases
+  as sequential role-switches inside its own context.
+- **No orphan agents** — every agent lives under the skill
+  that dispatches it.
+- **Output budget discipline** — agents have word budgets on
+  their reports.
+
+## Profile layer (project-specific)
+
+The profile fills slots that the plugin's prose references
+generically. Concretely:
+
+- **Paths**: `spec_dir`, `plan_dir`, `design_ledger`,
+  `design_contracts`, `design_models`, `code_roots`, `bench_dir`.
+- **Commands**: `build`, `test`, `lint`, `regression` (list).
+- **Vocabulary**: `cycle`, `subcycle`, `ledger_entry`.
+- **Naming**: `counter_dirs`, `policy` (`stable_per_directory_4digit`
+  or `date_prefix` or `flat`).
+- **Standing reading**: `always` (a list), `by_role` (a map
+  from role to list).
+- **Git**: `main_sacrosanct` (bool, default true),
+  `only_orchestrator_commits` (bool, default true),
+  `issue_tracker.kind` (`gitea` / `github` / `linear` / `none`),
+  `issue_tracker.close_marker` (e.g. `"closes #N"`).
+- **Pipeline customisations**: per-phase `mandatory_before`,
+  `mandatory_at`, `boss_only`, `when` (a condition tag).
+
+The full schema lives in `profile-schema.md`. The functional
+starting template is `../templates/project-profile.yml`.
+
+## Resolution model
+
+The plugin uses **profile-driven prompts**, not template
+rendering. Each SKILL.md and agent file is generic prose that
+references the profile prosaically:
+
+> Write the spec to the directory configured under `paths.spec_dir`
+> in the project profile. Use the naming policy configured under
+> `naming.policy`.
+
+When Claude Code loads the skill, the project profile is in
+context (the skill body explicitly instructs the model to read
+it first). The model performs the substitution at read-time.
+This avoids a build step and keeps a single source of truth in
+the repo.
+
+## Sittenkodex split
+
+The plugin does **not** carry project-specific anti-patterns,
+feature-acceptance gates, or domain contracts. Those belong in
+the project's own `CLAUDE.md`. The plugin only carries the
+*universal* discipline constants (only-orchestrator commits,
+main sacrosanct, no orphan agents, agents-don't-call-agents)
+which are conditions for the plugin's own correctness.
+
+The relationship:
+
+- **Plugin** (this repo): mechanics, universal discipline
+- **Profile** (per project): slots — paths, commands,
+  vocabulary, naming, git conventions, pipeline customisations
+- **Project CLAUDE.md**: sittenkodex — domain-specific anti-
+  patterns and acceptance criteria
+
+## What's out of scope for this plugin
+
+- **Boss/autonomous-orchestrator mode**: AILang's `boss` skill
+  is gated to a user-invoked `/boss` for autonomous queue
+  execution. Whether that generalises across projects is
+  unclear (queue mechanics depend on issue-tracker semantics).
+  Not in the initial skeleton; possibly added later as
+  `skills/boss/` if a cross-project autonomous mode crystallises.
+- **Issue-tracker integration**: the plugin can read the
+  profile's `issue_tracker.kind` and adjust commit-marker
+  suggestions, but does not directly call Gitea / GitHub /
+  Linear APIs.