bug(git): other consumers still read a timed-out worktree list as an empty family #1430

Expected behavior

A git worktree list that times out is not read as "this checkout has no siblings".

Actual behavior

#1429 makes the Worktrees panel, GitBar and worktrees.read say a git timeout (#1250 row 11). The exported listWorktreesForCwd still returns [] on a timeout, and three other consumers read that as "no family":

• Conversations picker (src/main/conversations/family.ts:78-88): from a linked checkout, a main-checkout conversation drops out of the repository-scoped picker, and service.ts caches that discovery for 3 s. Nothing says so.
• Worktree activity (src/main/ipc/worktreeActivity.ts:11-19): answers { ok: false }, the same as "not a repository".
• Agent activity repo root (src/main/index.ts resolveRepoRoot): falls back to the cwd, so a worktree's activity is not folded into its repository.
• Renderer history context (initialHistory.ts, history.ts) passes [] to ingestWorktreeRawEvent. A later live catalog refresh may correct it.

Each self-heals on the next successful call, but none is told. Found by #1429 review b (temp/review-1429/report-b.md, findings 2 and 3).

Fix direction

• Export listWorktreesForCwdDetailed (it exists in fix(git): a git timeout is said, never read as clean or not-a-repo (#1250 row 11) #1429) and have each consumer act on timedOut: do not cache the conversation family; answer timedOut from worktree activity; retry the repo-root resolution rather than record the cwd.
• Pin each with the git.timeout.test.ts execFile fake from fix(git): a git timeout is said, never read as clean or not-a-repo (#1250 row 11) #1429.

Related: #1250, #1429.