feat(catalog): add Spec Kit Schedule (schedule) community extension (#2473)

* feat(catalog): add Spec Kit Schedule (schedule) community extension

CP-SAT scheduler for spec-kit projects with multi-agent task
optimization. Adds catalog entry for v0.5.2 release.

Pre-flight verification:
- archive/refs/tags/v0.5.2.zip resolves (HTTP 200, 718322 bytes,
  SHA-256 00d4dab1df680e5888e0d0e861eb4696ace00661d40669bf719a75dc379b40b5)
- extension.yml schema_version 1.0, id 'schedule', 3 commands
  (speckit.schedule.run, speckit.schedule.portfolio, speckit.schedule.visualize)
- 566 tests passing on Ubuntu 3.10/3.11/3.12 + macOS 3.12 (all blocking)
- 92.51% line coverage, mypy --strict on 28 modules
- Sigstore attestations via attest-build-provenance@v2 (gh attestation
  verify exit 0 confirmed)
- 4 worked examples + replan demo runnable via bash bin/run-examples.sh

License: MIT
speckit_version: >=0.4.0

* fix(catalog): update Spec Kit Schedule entry to v0.5.3

v0.5.2 had two real-world install bugs caught when a user tried the
documented commands:

1. README/INSTALL showed 'specify extension add --from URL' (missing
   the EXTENSION positional arg). The canonical form is
   'specify extension add schedule --from URL'. Fixed in v0.5.3.

2. Release zip was ~5x bigger than peer extensions due to dev cruft
   (.github/, tests/, benchmarks/, build metadata). Added .gitattributes
   export-ignore in v0.5.3, dropping the zip from 718 KB to 590 KB.

v0.5.3 archive verified HTTP 200, sigstore attestations active.

* fix(catalog): bump Spec Kit Schedule entry to v0.5.4

Adds an opt-in after_tasks hook so users get prompted to run the
scheduler immediately after /speckit.tasks, without forcing it.
Mirrors the canonical pattern used by the bundled 'git' extension.

* fix(catalog): bump Spec Kit Schedule entry to v0.5.5

Documents the after_tasks hook in README and rewrites the
/speckit.schedule.portfolio command to autodetect the project's
tech stack via solver.autodetect, then refine interactively
against the matching recipe in docs/portfolio-design.md, instead
of starting from a blank slate.

* fix(catalog): bump Spec Kit Schedule entry to v0.6.0

State now encapsulated under .specify/, /speckit.schedule.run is
idempotent with auto-bootstrap, and portfolio detection is
AI-aware (reads .specify/integration.json and discovers the user's
fleet from the canonical location for whichever spec-kit AI
assistant they chose: claude, copilot, cursor-agent, gemini, or any
of the other 26 supported integrations).

* fix(catalog): bump Spec Kit Schedule entry to v0.6.1

Per-AI portfolio templates with verified May 2026 GA models
(gpt-5.5 flagship, claude-opus-4-7, gemini-2.5-flash). Critical
price unit fix (cost_aware reported $ figures 1000× inflated
in v0.6.0). Plus calibration feedback loop and inline summary.

* fix(readme): add Spec Kit Schedule row to Community Extensions table

Per Copilot review on PR #2473: the publishing guide requires an
accepted submission to update both extensions/catalog.community.json
AND the root README's Community Extensions table. Without the README
row the extension wouldn't appear in the primary browsable list.

Inserted alphabetically between 'Spec Diagram' and 'Spec Orchestrator'.
Category: process. Effect: Read+Write.

* fix(catalog): provides.commands 3→4 (schedule only) + bump top-level updated_at

Surgical edit responding to two Copilot review nits on PR #2473.
Previous attempt used str.replace too broadly and was reverted —
this version uses unique anchors to mutate only the schedule
entry and the top-level updated_at field.

1. extensions/catalog.community.json schedule entry had
   provides.commands: 3, but the extension exposes 4 commands
   (run, portfolio, visualize, calibrate — calibrate was added
   in v0.6.0 Build 2 / calibration feedback loop).

2. Top-level catalog updated_at was 2026-05-06T22:28:55Z but
   per-entry updated_at for our schedule entry is 2026-05-07.
   Since this PR modifies the catalog, the top-level timestamp
   advances too.

* fix(catalog): bump Spec Kit Schedule entry to v0.6.2

Adds /speckit.schedule.status (5th command) — self-diagnose
installation state, distinguishes 'expected-missing' (will
bootstrap automatically) from 'missing' (real problem). Closes
the audit-tool false-alarm gap where schedule-config.yml absence
post-install was misread as broken state.

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Co-authored-by: Julio César Franco Ardila <noreply@anthropic.com>