chore(pm): document decision-record PRs land as docs (PR-title vs commit-type)

[aleskalfas]

What

Direction B for #236: reconcile the commit/branch type vocabulary (which includes decision) with the PR-title pattern (standard CC set only) by documenting the deliberate mismatch — no pattern change.

Under squash-merge the PR title becomes the landed commit, so decision-record PRs are deliberately titled docs(<scope>): ... to keep git log on standard Conventional-Commits types (changelog/tooling-safe). A decision/<n>-... branch stays permitted; its PR lands as docs(...).

Changes (documentation only)

• titles.yaml pr entry — description expanded + good/bad examples (docs(decisions): ... good; decision(pm): ... bad).
• git-conventions.yaml branch-name entry — branch-vs-PR-title asymmetry note; fixes a pre-existing self-contradictory sentence (said a PR takes the decision type — corrected to branch).
• Capability README — new PR-title conv-types subsection.

Doc impact

This PR is the doc change. No regex/validation/severity/schema_version change.

Surface / version

Non-surface — documentation inside schema description/examples fields; patterns unchanged. No .pkit/VERSION bump, no migration (confirmed).

Follow-up (flagged, not in this PR)

COR-008 (core) lists decision as a commit type without noting the squash-merge PR-title=docs interaction; a one-line clarifying note there would close the loop — left as a follow-up (core record, out of scope here).

Verification

• pkit schemas validate -> all pass; pkit migrations check-diff -> no triggers; pkit refs validate -> no new findings.

Closes #236.

[aleskalfas]

Reviewer agent (local, reviewer): APPROVED

• Branch shape ([project-management:DEC-013-branch-and-pr-conventions], git-conventions.yaml branch-name): chore/236-reconcile-commit-type-vocabulary-with matches ^(feat|fix|docs|test|refactor|chore|ci|decision)/[0-9]+-[a-z0-9][a-z0-9-]*$. pass.
• Branch-type / issue-type alignment (same record + classification.yaml pr_type_mapping): issue [Task] Reconcile commit-type vocabulary with the PR-title pattern #236 carries type:maintenance, which maps to chore; the branch <type> is chore. pass.
• PR title is Conventional Commits ([COR-008] + DEC-013, titles.yaml pr): chore(pm): document decision-record PRs land as docs (PR-title vs commit-type) parses as <type>(<scope>): <desc> with chore in the standard set. pass.
• PR title type matches issue type (pr_type_mapping): type:maintenance → chore; title type is chore. pass.
• Issue classification complete ([project-management:DEC-012-classification-axes]): [Task] Reconcile commit-type vocabulary with the PR-title pattern #236 carries type:maintenance, priority:Low, and workstream:capabilities. pass.
• PR body links a closing issue (DEC-013 pr-body): Closes #236. present and closingIssuesReferences populated. pass.
• Surface-change discipline ([COR-010]): diff touches only description/examples prose in titles.yaml and git-conventions.yaml plus a README subsection — no renames/removals, no schema_version bump (stays 1), no regex/validation/severity change. No migration required. pass.
• No-shared-files invariant ([COR-001]): all edits land in capability-owned files under .pkit/capabilities/project-management/; no core-owned (*/core/) or installed-tree files touched. pass.

Notes (non-blocking):

• The change is genuinely documentation-only and internally consistent — the titles.yaml pr entry, the git-conventions.yaml branch-name asymmetry note, and the README subsection now agree that decision is a branch/commit type but decision-record PR titles land as docs(...). The prior self-contradictory "a PR takes the decision type" sentence is correctly repaired to "branch".
• The PR flags a follow-up to add a clarifying note to COR-008 (core) about the squash-merge PR-title=docs interaction, explicitly deferred as out of scope. That is a reasonable scoping call and not a gate concern here.