feat: editable route on page create

[NagariaHussain]

Why?

Closes #714.

The new-page dialog only asked for a Title. The URL was derived behind the author's back from the folder hierarchy, and renaming the page later silently moved it. Authors never saw the URL they were creating and couldn't choose it.

What?

The dialog now has a Route field that fills in from the title as you type and stops tracking it the moment you edit it by hand — the same interaction the new-space dialog already has.

• The prefilled default is still the hierarchy path (docs/guides/advanced/caching). Want a flat URL? Delete the middle segments.
• A route already in use is flagged inline while you type, instead of failing at merge time.
• Once the page exists the route is sticky: renaming the title no longer moves it. Changing the URL is an explicit edit through the existing route control.
• Existing documents are untouched — no migration, no broken URLs.

How?

• sanitize_route() normalises every author-supplied route through the app's existing slug rule, so a hand-written route can't produce a URL a derived one couldn't.
• check_route_available() (new whitelisted read) checks live documents and, when one exists, the change request's own staged items. It's space-scoped with an optional cr_name because the draft CR is created lazily — the dialog can open before one exists. Only the newest in-flight check is allowed to write the result, so a stale reply can't block a valid route.
• create_cr_page gains a route param; the batch create_node op already forwarded one.
• _update_cr_item's recompute_route path is gone.
• The route prefix is derived client-side: a group's route already carries the space route plus every ancestor slug, so a child's prefix is just the parent's route (the space root, whose own route is a bare slug, is the one exception). No round-trip per keystroke, and it works when the parent group is itself an unsaved draft.

Spec: specs/editable_page_route.md.

Testing

• 4 backend cases in test_wiki_change_request.py (route honoured, route sanitised, rename-keeps-route regression, availability across live + CR). The rename regression was verified by temp-reverting the fix.
• e2e e2e/tests/page-route-editable.spec.ts covers prefill → auto-track → manual override → save.

🤖 Generated with Claude Code

https://claude.ai/code/session_01Dn1ETNV7ufoM8xA6FCLnnE

[greptile-apps]

Confidence Score: 4/5

Not safe to merge until saving waits for pending route validation.

A duplicate route can still be submitted during the debounce or network window and fail only when merged.

Files Needing Attention: frontend/src/composables/useTreeDialogs.js

_{Reviews (2): Last reviewed commit: "refactor(route): use ErrorMessage for th..." | Re-trigger Greptile}