refactor: Automatic Safe-Name Conversion at Naming Entry Points

[sahil-noon]

Meta

Change ID	Type	Confidence	Plan	Review
ln4n	refactor	3.6/5.0	12/12 tasks, 17/17 acceptance ✓	✓ 1 cycle

Impact	+/−	Net
raw	+990 / −66	+924
true	+556 / −55	+501
└ impl	+236 / −52	+184
└ tests	+320 / −3	+317

_{excludes fab/, docs/ · generated by fab-kit v2.16.5}

Pipeline: intake ✓ → apply ✓ → review ✓ → hydrate ✓ → ship → review-pr

Summary

run-kit's name validation was inconsistent and leaky: ValidateName allowed spaces in session/window names (which then broke tmux CLI targeting, session-group naming, and URL routing), while server names were rejected outright on a typed space. This change adds automatic, live, per-name-kind safe-name conversion in the frontend (e.g. "My problem" → "My_problem" as you type) and tightens the backend so new-name validation rejects spaces as a real contract, while existing-name lookups stay permissive for names created outside run-kit.

Changes

• Shared frontend name-transform module — app/frontend/src/lib/names.ts (new), promoting toTmuxSafeName() out of create-session-dialog.tsx into one canonical transform per name kind (toSafeSessionName, toSafeWindowName, toSafeServerName, toSafeWorktreeName)
• Live in-input conversion at every naming entry point: create-session/window dialog, session rename dialog, sidebar inline renames, top-bar WindowHeading inline rename, server-name input, worktree-name field
• Backend: ValidateName tightens for NEW names (rejects spaces); existing-name lookups stay on the permissive validator so pre-existing spacey names remain operable
• Tests and companion docs: Vitest coverage for each transform, Go table tests for the tightened validator, Playwright e2e updates (window-heading.spec.ts + .spec.md, sync-latency.spec.ts + .spec.md)