feat(tags): add autocomplete to tags input

[axelav]

Summary

• Add GET /api/tags/search?q= endpoint that returns matching tags as HTML buttons, scoped to the authenticated user
• Add vanilla JS autocomplete on the entry form tags input with debounced fetch, keyboard navigation (arrow keys, enter, escape), click-to-select, and client-side filtering of already-entered tags
• Add dropdown CSS matching the existing design system

Test Plan

• 4 new integration tests: auth required, prefix matching, empty results, user scoping (92 total, all passing)
• Manual: go to /entries/new, type a tag prefix, verify dropdown appears after 300ms
• Manual: arrow keys highlight items, Enter selects, Escape closes
• Manual: clicking a suggestion inserts it with trailing comma
• Manual: already-entered tags are excluded from suggestions
• Manual: edit an existing entry — autocomplete works the same way

[Copilot]

Pull request overview

Adds tag autocomplete for the entry form by introducing a tag search API endpoint and wiring up client-side dropdown behavior/styling.

Changes:

• Add GET /api/tags/search?q= to return matching tags (scoped to the authenticated user) as an HTML fragment.
• Add vanilla JS autocomplete behavior to the entry form tags input (debounced fetch + keyboard/click interactions).
• Add CSS styling for the autocomplete dropdown; add integration tests for the new endpoint.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/routes/tags.rs	Adds /api/tags/search route + handler that queries user-scoped tags and renders HTML buttons.
templates/entries/form.html	Wraps tags input and adds JS to fetch/render suggestions and support keyboard/click selection.
static/style.css	Adds dropdown and item styling for tag autocomplete UI.
tests/tags.rs	Adds integration tests covering auth, matching, empty results, and user scoping for tag search.
docs/plans/2026-02-17-tag-autocomplete.md	Documents the implementation plan and test plan for the feature.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

The LIKE pattern is built directly from user input, so % and _ in q act as wildcards (e.g., q=% returns arbitrary tags) and the behavior is no longer strict prefix matching. Escape %/_ in the prefix (and use ... LIKE ? ESCAPE '\\'), or switch to a safer prefix predicate if available for the chosen DB/collation.

[Copilot]

The fetch chain doesn’t handle non-OK responses or redirects (e.g., an expired session will redirect to /login, and the login HTML may be rendered inside the dropdown). Check r.ok/r.redirected (or r.status === 401 if you change the API behavior) and hide the dropdown / trigger a navigation to login instead of blindly rendering r.text().

[Copilot]

There’s a race condition between in-flight requests: a slower response for an older segment can arrive after a newer one and overwrite the dropdown with stale suggestions. Consider using AbortController to cancel the previous request, or track an incrementing request id and ignore responses that aren’t the latest.