feat: replace global issue lock with keyed persistent store (Closes #443)

Store per remote/org/repo/issue locks under GITEA_ISSUE_LOCK_DIR with
atomic writes and per-session binding. Integrate own-branch adoption for
lock recovery, update worktree-start and cleanup reconcile, and add tests
documenting the ban on manual global lock seeding.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

scripts/worktree-start

@@ -38,13 +38,21 @@ fi
 branch="$1"
 start_ref="${2:-prgs/master}"
 
+script_dir="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+repo_root="$(cd "$script_dir/.." && pwd)"
+
 # Enforce issue-linked, traceable branch names (issue → branch → worktree → PR).
 if [[ "$allow_unlinked" -eq 0 ]]; then
-  if [[ ! -f "/tmp/gitea_issue_lock.json" ]]; then
-    echo "Error: Issue lock file '/tmp/gitea_issue_lock.json' is missing. You must lock exactly one issue before branch creation (fail closed)." >&2
+  locked_branch=$(python3 -c "
+import sys
+sys.path.insert(0, '$repo_root')
+import issue_lock_store
+print(issue_lock_store.resolve_locked_branch_for_session('$branch'))
+")
+  if [[ -z "$locked_branch" ]]; then
+    echo "Error: No session issue lock is bound. Call gitea_lock_issue before branch creation (fail closed)." >&2
     exit 2
   fi
-  locked_branch=$(python3 -c "import json; print(json.load(open('/tmp/gitea_issue_lock.json')).get('branch_name', ''))")
   if [[ "$branch" != "$locked_branch" ]]; then
     echo "Error: Requested branch '$branch' does not match locked branch '$locked_branch' (fail closed)." >&2
     exit 2
@@ -68,8 +76,6 @@ EOF
   fi
 fi
 
-script_dir="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
-repo_root="$(cd "$script_dir/.." && pwd)"
 worktree_name="${branch//\//-}"
 worktree_path="$repo_root/branches/$worktree_name"