enhance(#3587): add a per-phase commit_docs override (#3601)

* feat(#3587): add a per-phase commit_docs override

Delivers epic #2292's second user story: commit an architecture phase's
artifacts while execution phases stay local. commit_docs was project-wide and
binary, so the only choices were all phases or none.

Shape is a config dynamic key phase_commit_docs.<phase-id>, following the 14
existing dynamicKeyPatterns precedents rather than inventing a PLAN.md
frontmatter spec -- which #2292 itself flags as becoming its own maintenance
surface.

Tier 1 resolves in cmdCommit, NOT in loadConfig: loadConfig has no phase
context and is called by nearly every command, so threading one through it to
serve a single caller would be a far larger blast radius for no gain. The phase
comes from detectPhaseNumberFromFiles, which cmdCommit already computes for
branch naming and which is already hardened against the #2539 project-code bug.

Suppression by the per-phase tier returns its own reason rather than reusing
skipped_commit_docs_false -- telling a user their project setting is false when
it is true would be actively misleading. Additive; the two existing reason
strings that agents/gsd-executor.md matches on are unchanged.

The manifest's phase-id pattern is a hand-copy of PHASE_NUMBER_TOKEN_SOURCE
because the manifest is hand-maintained JSON, so a behavioral parity test
asserts both surfaces accept and reject the same token shapes.

* fix(#3587): fold tests, close review findings, update reference docs

Fold: the new tests were added as their own file, which required loosening a
grandfathered lint-test-file-count bucket 5-to-6. A ratchet exists to go down
only. commit-docs-bypass.test.cjs is the established commit_docs test home and
already hosts two folded suites, so the tests fold there as a third block and
the allowlist is reverted untouched.

Standards review: CONTEXT.md and the test header both cited a
phase-commit-docs-manifest-parity.test.cjs that never existed; a repo-wide
sweep found a fourth stale cite in the schema manifest description. All four
now name the real location.

Spec review: the issue's Scope of changes named planning-config.md and
git-planning-commit.md and neither was touched. Both now document the four-tier
precedence and the new skip reason.

Security review, minor and unproven: detectPhaseNumberFromFiles returns the
FIRST matching path's phase, so a --files list spanning two phases resolves the
override against whichever comes first. That helper is hardened and widely used,
so it is not changed; the behavior is pinned by a named test and disclosed in
the design and user docs. A pinned behavior is not a bug; an unpinned surprise
is.

* chore(#3587): backfill changeset pr number to 3601

---------

Co-authored-by: sim <sim@local>

gsd-core/references/planning-config.md

@@ -76,6 +76,8 @@ if [[ "$INIT" == @file:* ]]; then INIT=$(cat "${INIT#@file:}"); fi
 
 **Auto-detection:** If `.planning/` is gitignored, `commit_docs` is automatically `false` regardless of config.json. This prevents git errors when users have `.planning/` in `.gitignore`.
 
+**Per-phase override:** `phase_commit_docs.<phase-id>` (e.g. `phase_commit_docs.03`) overrides `commit_docs` for one phase only, and wins over both the explicit config value and gitignore auto-detection — see `docs/CONFIGURATION.md#per-phase-override-phase_commit_docs` for the full precedence chain and examples.
+
 **Commit via CLI (handles checks automatically):**
 
 ```bash
@@ -380,7 +382,7 @@ These can be set at top level or nested under `planning.*` (e.g., `"planning": {
 
 Several config fields affect each other or trigger special behavior:
 
-1. **`commit_docs` auto-detection** -- When no explicit value is set in config.json and `.planning/` is in `.gitignore`, `commit_docs` automatically resolves to `false`. An explicit `true` or `false` in config always overrides auto-detection.
+1. **`commit_docs` resolution chain** -- Four tiers, highest wins: (1) `phase_commit_docs.<phase-id>` for the phase being committed, (2) an explicit `commit_docs` (or `planning.commit_docs`) value in config.json, (3) `.gitignore` auto-detection (`.planning/` in `.gitignore` resolves to `false`), (4) the manifest default (`true`). Precedence: per-phase → explicit config → gitignore auto-detect → default.
 
 2. **`branching_strategy` controls branch templates** -- The `phase_branch_template` and `milestone_branch_template` fields are only used when `branching_strategy` is set to `"phase"` or `"milestone"` respectively. When `branching_strategy` is `"none"`, all template fields are ignored.