Add user profiles

[llbbl]

Summary

• Add authenticated user profile settings, avatars, themes, and notification preferences.
• Broadcast presence through the WebSocket server and expose public profile lookup APIs.
• Provide matching Vue and Svelte profile panels with integration coverage.

Changes

Backend

• app/Controllers/Profile.php: Add HTML and API profile, avatar, and public-profile endpoints.
• app/Models/UserModel.php: Persist profile fields, presence, and trimmed public-profile lookups.
• app/Libraries/ChatWebSocketServer.php: Track authenticated presence across multiple connections.
• app/Database/Migrations/2026-09-15-000000_add_user_profile_fields.php: Add profile columns to users.

Frontend

• src/vue/ProfilePanel.vue: Add Vue profile editing and presence controls.
• src/svelte/ProfilePanel.svelte: Add Svelte profile editing and presence controls.
• src/js/profile.js: Share profile API, CSRF, theme, and avatar helpers.
• src/css/chat.scss: Style profile panels, avatars, themes, and presence state.

Documentation and tests

• docs/user-profiles.md: Document profile behavior and API usage.
• tests/Tests/Integration/ProfileIntegrationTest.php: Cover profile and avatar endpoints.
• tests/Tests/Integration/UserProfileRepositoryIntegrationTest.php: Cover profile persistence and lookup trimming.
• tests/Tests/Integration/WebSocketFlowIntegrationTest.php: Cover multi-connection presence lifecycle.

Review follow-ups

• Frontend profile lookups now avoid repeated fetches.
• Server profile username lookups now trim and normalize input before querying.
• Legacy Chromium E2E selectors are scoped away from DebugBar controls, and scenario data is isolated.

Validation

• composer test:integration: OK (25 tests, 139 assertions)
• composer test:integration:websocket: OK (5 tests, 33 assertions)
• composer test:all: OK (204 tests, 692 assertions)
• ./vendor/bin/phpstan analyse --memory-limit=256M --debug --no-progress: OK
• pnpm check: OK
• pnpm e2e: PASS (6 tests; local Chromium validation)
• ./vendor/bin/php-cs-fixer fix --dry-run --diff --sequential: OK (composer cs-check parallel mode hit local EPERM, sequential check passed)
• pnpm build: OK (required normal pnpm store/cache access after sandboxed run reported unable to open database file)
• Biome: PASS
• Mutation testing: Not run because the mutation workflow is manual-only by user request.

Closes #126