run start: lint declared targets against project roots and adapter id conventions

[geuben]

Summary

• Adds static target lint at tdd plan register and tdd run start (before the baseline claim) to catch two shapes of plan-author error before anything executes: (1) a target path that duplicates the project's root prefix, and (2) a separator spelling that can never match the adapter's collected-id grammar
• Grammar rules per adapter: pytest (:: required), vitest (> required), gradle (/ required), xctest (three /-separated parts required); exec has no grammar rule
• Root-prefix rule: when project.root != "." and the target's path starts with root/, flag it with a suggestion — unless the actual nested directory exists in the worktree (the filesystem-existence exemption passes genuine root/root/… paths)
• Both gates refuse with reason: "target_lint" and a structured findings list; run start re-lints the stored contract against the current config to catch root/adapter drift since registration

Commits

673c8c8 docs: friction log for issue-71-target-lint
46bf7ca docs: extend register and run-start PRD rows with target lint
43bd20f feat: target lint gates run start before the baseline claim
e65bcbe test: run start re-lints the stored contract against current config
6fe3b74 refactor: register refuses a root-duplicated vitest target
503d5b8 refactor: a genuinely nested root-named path is not flagged
0aaf325 refactor: register refuses a target that duplicates the project root prefix
b6bcb78 feat: xctest lint_target_id flags ids without three slash-parts
baa62cc test: xctest grammar lint requires Bundle/Class/testMethod
b1b852 feat: gradle lint_target_id flags ids missing the / separator
58ea0fd test: gradle grammar lint requires the classname/method slash
aae238f refactor: a vitest target without ' > ' is flagged by the grammar hook
4ffdbf0 feat: vitest lint_target_id flags ids missing ' > '
7c997c0 test: vitest grammar lint requires the ' > ' separator
c1b262f feat: target lint — adapter id-grammar hook, wired into plan register
d6a8433 test: plan register refuses a pytest target with no ::

Test coverage note

All decision-point operators in new code are covered by at least one test (pseudo-mutation analysis passed). 8 cycles declared and delivered, 0 skipped. 3 red-first violations handled via sensitivity checks (cycles 5, 6, 7 passed on arrival due to complete implementation in cycle 1).

Closes #71