fix(investigate): resolve the scope lock to an absolute path and release it in Phase 5 (#2845) - #2846

$ HOOK=~/.claude/skills/gstack/freeze/bin/check-freeze.sh
$ T=$(mktemp -d); mkdir -p $T/state $T/wt-a/src $T/wt-b/src $T/wt-b/scratch
$ echo "src/" > $T/state/freeze-dir.txt
$ (cd $T/wt-a && printf '{"tool_input":{"file_path":"%s/wt-a/src/a.ts"}}' $T | GSTACK_HOME=$T/state bash $HOOK)
{}
$ (cd $T/wt-b && printf '{"tool_input":{"file_path":"%s/wt-a/src/a.ts"}}' $T | GSTACK_HOME=$T/state bash $HOOK)
{"hookSpecificOutput":{"hookEventName":"PreToolUse","permissionDecision":"deny","permissionDecisionReason":"[freeze] Blocked: .../wt-a/src/a.ts is outside the freeze boundary (.../wt-b/src). Only edits within the frozen directory are allowed."}}
$ (cd $T/wt-b && printf '{"tool_input":{"file_path":"%s/wt-b/scratch/notes.md"}}' $T | GSTACK_HOME=$T/state bash $HOOK)
{"hookSpecificOutput":{"hookEventName":"PreToolUse","permissionDecision":"deny","permissionDecisionReason":"[freeze] Blocked: .../wt-b/scratch/notes.md is outside the freeze boundary (.../wt-b/src). ..."}}

# state file holding the absolute path instead: verdicts no longer depend on cwd
$ echo "$T/wt-a/src/" > $T/state/freeze-dir.txt
$ (cd $T/wt-b && printf '{"tool_input":{"file_path":"%s/wt-a/src/a.ts"}}' $T | GSTACK_HOME=$T/state bash $HOOK)
{}
$ (cd $T/wt-b && printf '{"tool_input":{"file_path":"%s/wt-b/src/b.ts"}}' $T | GSTACK_HOME=$T/state bash $HOOK)
{"hookSpecificOutput":{"hookEventName":"PreToolUse","permissionDecision":"deny","permissionDecisionReason":"[freeze] Blocked: .../wt-b/src/b.ts is outside the freeze boundary (.../wt-a/src). ..."}}

$ bun test test/investigate-freeze-path.test.ts
(fail) investigate scope lock is absolute and released (#2845) > investigate/SKILL.md resolves the lock directory to an absolute path before writing it
(fail) investigate scope lock is absolute and released (#2845) > investigate/SKILL.md skips the lock loudly when the directory does not resolve
(fail) investigate scope lock is absolute and released (#2845) > investigate/SKILL.md releases its own lock in Phase 5, by compare-and-delete
(fail) freeze prose does not promise a session-scoped boundary (#2845) > freeze/SKILL.md
(fail) freeze prose does not promise a session-scoped boundary (#2845) > guard/SKILL.md
 11 pass
 5 fail

$ bun test test/investigate-freeze-path.test.ts
 16 pass
 0 fail
Ran 16 tests across 1 file. [1.78s]
$ bun run gen:skill-docs --dry-run | tail -3
FRESH: spec/sections/gate-and-file.md
FRESH: review/design-checklist.md
FRESH: lib/dom-dump.js

$ bun run test
[test:free] FAIL — 6 failing test(s) in 2 file(s), 0 crashed worker(s)
  ✗ test/gstack-design-detect.test.ts (3)
  ✗ test/gstack-artifacts-init.test.ts (3)
6 shards, 6 failures. The other 4 shards: PASS (1542 / 1212 / 1619 / ... tests).

# The same 6 fail on an untouched main checkout (71f6048) on this machine, and neither
# file references investigate/, freeze/ or guard/:
$ cd <clean main checkout> && bun test test/gstack-artifacts-init.test.ts test/gstack-design-detect.test.ts
 81 pass
 6 fail
Ran 87 tests across 2 files. [49.54s]
# artifacts-init: this machine's gh git_protocol is ssh; design-detect: local impeccable install state.
# Machine-specific, pre-existing, unrelated to this diff.