chore(pm): cache projects_v2_node_id to skip per-create gh project view read

[aleskalfas]

What

Cache the Projects-v2 project node id in adopter config so create-issue's board path skips a per-create gh project view round-trip.

• create-issue — _resolve_project_node_id reads config["projects_v2_node_id"] first; live-resolves via gh project view only on a miss (same id, cached). No output/behaviour change.
• bootstrap (greenfield) — populates the field into project/config.yaml at adoption when a board is configured (round-trip write preserves comments; idempotent); no-op in label-fallback mode.
• adopt-existing (brownfield) — resolves the id and surfaces it as a recommendation in the audit report + --json inventory. It does NOT write config, preserving the DEC-037 mutate-nothing invariant (draft-not-apply). The read-side slot in _lib/hooks.py already existed; this populates it.

Design note

adopt-existing recommends rather than writes (DEC-037 §1 forbids brownfield config mutation, enforced by tests); bootstrap does the write. A faithful reading of "populated at adoption" that respects the stronger invariant.

Doc impact

New optional projects_v2_node_id config field documented in the capability README config example (there is no JSON schema for config.yaml).

Surface / version

Capability-internal surface change: project-management component.version 0.44.0 -> 0.45.0 (minor). Backbone .pkit/VERSION unchanged (no dispatcher/COR/manifest change). Additive optional field -> no migration.

Verification

• targeted tests (create-issue/bootstrap/adopt-existing) -> 113 passed; full pm suite -> 1823 passed.
• cache-hit asserts zero gh project view calls; cache-miss falls back to live; bootstrap populates when board+uncached, skips otherwise.
• pkit schemas validate pass; pkit migrations check-diff -> no triggers; exec bits 100755 preserved.

Closes #310.

[aleskalfas]

Reviewer agent (local, reviewer): APPROVED

• Branch shape — chore/310-cache-projects-v2-node-id matches the <conv-type>/<issue-number>-<slug> pattern in git-conventions.yaml (branch-name). Pass.
• Branch-type / issue-type alignment — closing issue [Task] Cache projects_v2_node_id in config to avoid per-create gh project view read #310 carries type:maintenance, which maps to conv-type chore per classification.yaml pr_type_mapping; branch prefix is chore. Pass ([project-management:DEC-013-branch-and-pr-conventions]).
• PR title Conventional Commits — chore(pm): cache projects_v2_node_id to skip per-create gh project view read parses as <type>(<scope>): <desc> with chore in the accepted PR-title set. Pass (COR-008).
• PR title type ↔ issue type — chore is the mapped type for type:maintenance. Pass.
• Issue classification complete — [Task] Cache projects_v2_node_id in config to avoid per-create gh project view read #310 carries type:maintenance, priority:Low, workstream:decisions (plus state:in-progress); all three axes present. Pass ([project-management:DEC-012-classification-axes]).
• PR body links closing issue — Closes #310. present and closingIssuesReferences populated. Pass.
• Surface-change discipline — diff is an additive optional config field (projects_v2_node_id) with new resolver/persist helpers; no renames/removals in kit-owned trees, no schema_version bump (stays 2), no subtree restructure. The bump is component.version 0.44.0→0.45.0, not a schema bump. PR reports pkit migrations check-diff → no triggers; no migration required. Pass (COR-010).
• No-shared-files invariant — all edits are under the project-management capability tree (its own scripts, README, package.yaml) and tests/; no */core/-owned files touched. bootstrap's write targets the adopter-owned project/config.yaml, not a core-owned file. Pass (COR-001).

Note (informational, not gating): adopt-existing recommends rather than writes config, preserving the DEC-037 mutate-nothing posture — consistent with the review scope's expectation and out of scope for a correctness verdict. Every criterion resolves to pass; verdict follows mechanically.