Add worktree-aware autocomplete suggestions

[warp-agent-staging]

Summary

Adds worktree-aware autocomplete: in a repo with multiple git worktrees, Warp now suggests the repo's known worktrees while typing worktree-relevant commands, so you can jump to a worktree by its (often short/auto-generated) name from anywhere. Resolves #11542.

A worktree suggestion displays the worktree's memorable name and inserts its shell-escaped absolute path, so accepting one works regardless of the current directory. Suggestions augment (never replace) normal filesystem path completion.

Design decisions

Triage flagged product ambiguity; resolved here toward the smallest change that satisfies the issue, since the completion engine is shared and latency-sensitive:

• Trigger contexts: cd <arg> and the git worktree subcommands that reference an existing worktree (remove, move, lock, unlock, repair). git worktree add is intentionally excluded (it creates a new worktree).
• Insert value: the worktree's shell-escaped absolute path, displayed under its name — the checked-out branch's basename, falling back to the directory basename. This makes cd <name> resolve from any directory while keeping the list readable.
• Ranking / merge: worktree suggestions are appended to filesystem completion at default priority and de-duplicated by display name, so they supplement rather than reorder or replace normal completion.
• Data source & caching: a per-cwd, TTL-cached (5s) git worktree list --porcelain run through the session's existing command executor (works for local and warpified-remote sessions). The cache lives on the shared Session, so git is not spawned per keystroke — satisfying the no-latency-regression criterion.
• Feature-gated: behind FeatureFlag::WorktreeCompletions (added to DOGFOOD_FLAGS), so the shared completion path is inert until the flag is on.

Where the change lives

• crates/warp_completer — new engine/worktree.rs suggestion source + is_worktree_completion_context, a worktrees() method on PathCompletionContext, and injection at the end of argument completion (both v2 and legacy).
• app/src/completer/mod.rs — SessionContext::worktrees() (flag-gated) + the git worktree list --porcelain porcelain parser.
• app/src/terminal/model/session.rs — the per-cwd TTL cache and loader on Session.
• crates/warp_features/src/lib.rs — the WorktreeCompletions flag.

Verification

Deterministic (all passing):

• New unit tests for the suggestion source and context detection (crates/warp_completer/.../worktree_tests.rs).
• New end-to-end test through the public suggestions() API (crates/warp_completer/.../suggest/test.rs::test_worktree_completion_for_cd): proves worktree names surface for cd and git worktree remove, are prefix-filtered, and are excluded for unrelated commands — passing under both default and v2 feature configs.
• Porcelain parser tests (app/src/completer/test.rs).
• ./script/format clean; cargo clippy -p warp_completer / -p warp / -p warp_features (--all-targets --tests -D warnings) clean; cargo nextest run -p warp_completer (default + v2) and the -p warp parser tests pass.

Running-UI visual proof — outstanding (explicit exception)

This behavior is gated behind the dogfood-only WorktreeCompletions flag and exists only on this branch, so it can only be exercised by a from-source build of the GPU-based Warp desktop client with a live shell session and a repo containing multiple worktrees. This headless remote build environment cannot produce that runnable client, so per factory-ui-verification's explicit-exception path the running-UI capture is deferred to a human/dogfood build. The end-user behavior is otherwise covered end-to-end by the deterministic suggestions() pipeline test above (the same code path the UI invokes).

CHANGELOG-NEW-FEATURE: Autocomplete now suggests your repository's git worktrees when typing cd and git worktree commands.

Originating thread: https://warpdev.slack.com/archives/C0BDQDW8V5E/p1785969286177199

Conversation: https://staging.warp.dev/conversation/7d3911cb-16c7-468f-8fb8-8d6c7540a684
Run: https://oz.staging.warp.dev/runs/019fd420-7fa8-7268-b619-36dceccf018a

This PR was generated with Oz.

[warp-agent-staging]

Superseded / on hold: after review, this worktree-completion should instead be expressed as a dynamic generator in warpdotdev/command-signatures (attach a generatorName to cd.json's folders arg, and fill the worktree arg slot in git.json's worktree subcommands), following the shipped precedent of the git local_branches/tags/commits generators. This client-side approach in warpdotdev/warp is not the chosen path. Left open (not closed) pending the command-signatures implementation — a human decides whether to close.