feat!: mount pages 3.0.0 command, drop runCli integration

[harshitsinghbhandari]

Paired with agentlab-in/pages#3. Old/new are broken in both directions; land together, no release from this PR.

• vendor/pages repinned to 3.0.0 at 887e73f189c192423fd9f897730b06417fa82362 (pins.json version, commit, and package SHA updated; verify:pins passes).
• src/cli.ts: removed runCli import (deleted upstream). The router now mounts createPagesCommand() with addCommand and parses in process. Help, version, unknown-tool, stdio, and exit-status behavior preserved.
• tests/router.test.ts: version expectation updated; new test rejects top-level put (unknown tool).
• scripts/smoke-binary.sh: version and alab pages list assertions updated; new top-level put rejection check.
• docs/integration.md and docs/spec.md updated for the mount interface and pin.

Verification: bun install --frozen-lockfile, verify:pins, bun test (4 pass), bun build, compiled binary smoke test passed. No review tool added.