chore(workflow): declare carryctx for discovery and document global install

[Xuepoo]

Priority: P2 | Area: devtools | Labels: chore,area:devtools,P2 | Milestone: v0.1.0 | RFC: - | Task: m0291 (commander directive; no CarryCtx task or Issue created)

Context

Commander directive m0291: make the carryctx tool discoverable to anyone who
clones a Bitty repository, while keeping the globally installed CLI as the
recommended local development setup. Workflows stay public/visible in-repo.

Availability (verified)

• npm: carryctx@0.11.2, bin carryctx -> bin/carryctx.js. bun install
  pulls the platform binary and carryctx --version prints 0.11.2. Scoped
  names @carryctx/cli and @xuepoo/carryctx do not exist on npm.
• crates.io: carryctx 0.11.3 is published, but it is a binary-only crate
  (no library target) and this repository has no [package] entry for a
  [dev-dependencies] section, so no Cargo.toml reference is possible.

Change

• package.json: add carryctx@0.11.2 to devDependencies for discovery.
• bun.lock: regenerated with bun install (never npm).
• README.md / AGENTS.md: document that carryctx records tasks, decisions,
  and checkpoints; that the recommended local setup is the global install
  (cargo install carryctx or npm i -g carryctx); and that the full
  workflow is visible in-repo on refs/heads/carryctx-snapshots
  (just workflow-import).

Gates

• bun install --frozen-lockfile: pass (no changes)
• repository quality gates: pass

Not self-merged; left for commander review.

[Xuepoo]

Owner: m0291 (CarryCtx discoverability). No dedicated Issue/CTX for this standalone docs+devDependency change; ownership is recorded here per closeout policy rather than creating a per-repo tracking issue.