feat: v0.6.0 — routing receipts, branch review, agent comparison, uni…

[ThisaST]

…fied task UI

Fixes four bugs found while verifying the app against a live Claude Code CLI:

• Orchestration failed on the shipped default config. With one installed CLI (maxConcurrent 1, maxParallelTasks 2), the first lane marked the provider busy before the second ranked, so the second subtask died with "No eligible provider". Lanes now wait for a slot; only a subtask no idle provider could take is a real failure.
• The synthesizer redid all subtask work in the main working tree. It is a full agent with file tools, and seeing the worktree files "missing" it recreated them, defeating the isolation and paying twice. The synthesis prompt now states it is a read-only reporting step and names the committed branches.
• Changed files were unopenable when the workspace root is reached through a symlink. CLIs report canonical paths, which the lexical containment check read as an escape. Containment is now checked against both views of the root; traversal is still rejected.
• JsonStore.save raced with itself. Concurrent saves shared one temp filename, so overlapping renames lost a write and threw ENOENT. Saves are serialized and each gets its own temp file.

Adds:

• Routing receipts. routeTask returns the ranking and its explanation in one pass, so the per-task score breakdown can never drift from the real decision.
• Branch review inbox (src/main/branches.ts). Lists frontier/* branches per repo with diffs, merge, and delete. Only frontier/ branches can be touched, merging is refused on a dirty checkout, and conflicts abort rather than half-apply.
• Head-to-head comparison. One prompt to several agents at once, each in its own worktree branch, with no failover — a failed lane is a result about that agent.
• Unified task surface. The duplicated split-pane and detail-page renderers are replaced by one surface with Conversation, Files, and Route tabs. Providers and Usage merge into Agents; a Mission Control home shows live agent capacity.
• Provider cards no longer rebuild on every streamed chunk, which used to discard whatever the user was typing.
• Refreshed the Claude model list (opus-5, sonnet-5), verified against the CLI.

Verified live against Claude Code 2.1.220: streaming, session resume, file edits, control-plane injection, cancellation, and both orchestration paths.

105 tests pass, typecheck and build clean.