docs: skills + revisions + proposals reference, plus cheatsheet update

Phase 7 of the Skills + Revisions + Proposals work — documentation
pass for the surface added in PR-1 through PR-6. Reference material
only; no code changes.

## What's added

- `docs/skills.md` — skill model, scoping rules, CLI surface, the
  `mcpctl config claude --project` setup flow, metadata schema (with
  the deferred-execution note for hooks/mcpServers/postInstall), the
  on-disk state file shape, atomic install mechanics, failure
  semantics, and what's deferred.
- `docs/revisions.md` — ResourceRevision model, semver auto-bump
  rules, contentHash diff key (cross-resource sync), CLI for history
  / diff / restore, RBAC, audit emission, storage growth note.
- `docs/proposals.md` — ResourceProposal model, the reviewer flow
  (CLI + web UI), atomic-approval mechanics, the propose_prompt /
  propose_skill MCP tools, the propose-learnings global skill that
  steers Claude toward engaging with them, and the deferred legacy
  PromptRequest cutover.

## What's edited

- Top-level `CLAUDE.md` — resource cheatsheet adds `skill`, `proposal`,
  `revision` with cross-references to the new docs. The legacy
  `promptrequest` entry stays (still on the legacy code path) but
  notes that new work should use `proposal`.

## What's NOT in this PR

- The PromptRequest → ResourceProposal cutover migration. Both run
  side-by-side today; the focused cutover PR will rename + backfill +
  drop. Keeping that out of PR-7 means review can stay on docs.
- Bundle-backup / `mcpctl apply -f` skill support (deferred from PR-3).
- `metadata.hooks` / `metadata.mcpServers` / `metadata.postInstall`
  execution (deferred from PR-5).
- Existing-page UI migration to Tailwind (deferred from PR-6 — old
  inline-styled pages coexist fine inside the new Layout).

These are tracked as future PRs; each is its own focused change.

## Verification

`pnpm test:run` whole monorepo: 162 test files / 2157 tests green.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -35,6 +35,9 @@ Key routing rules:
 - `project` — workspace grouping servers, prompts, agents
 - `llm` — server-managed LLM provider (api key + endpoint)
 - `agent` — LLM persona pinned to one Llm; project attach surfaces project Prompts as system context, project MCP servers as tools, and exposes the agent itself as an MCP virtual server (`agent-<name>/chat`). See `docs/agents.md`, `docs/chat.md`.
-- `prompt` / `promptrequest` — curated content / pending proposal
+- `prompt` / `promptrequest` — curated content / legacy pending proposal (use `proposal` for new work).
+- `skill` — Claude Code skill bundle (SKILL.md + files + typed metadata). Materialised onto disk by `mcpctl skills sync`. See `docs/skills.md`.
+- `proposal` — generic pending proposal queue, replaces `promptrequest`. Covers both prompts and skills. See `docs/proposals.md`. Triage via `mcpctl review`.
+- `revision` — append-only audit + diff log shared by prompts and skills. Auto-bumps semver on save. See `docs/revisions.md`.
 - `rbac` — access control bindings
 - `mcptoken` — bearer credentials for HTTP-mode mcplocal