Design logged-in seating layout preview webpage with CSV import and interactive editing

[cycomachead]

Add logged-in seating layout preview with CSV import and interactive editing

Adds a standalone page (/layouts/preview/) where a logged-in user can upload or paste a room CSV, see the seating layout rendered without saving anything to the database, highlight seats by layout or attribute, and toggle seats individually to build and export a new layout. Also scaffolds a dev login for non-staging/production environments and fixes an icon-rendering bug in the header.

Changes

• New preview page (/layouts/preview/, login required): accepts CSV upload or pasted text, parsed through the same parse_csv/prepare_seat path as the room import flow. Nothing is persisted.
• Rendering — fixed seats drawn in a mirrored grid matching the existing room view; movable seats grouped by attribute set.
• Highlight dropdown grouped into Layouts / Handedness / Condition / Placement & Use, with per-attribute seat counts.
• Schema clarity (server/services/core/layout_preview.py) — introduces a closed vocabulary of canonical seat attributes (physical properties like lefty, broken, aisle, dsp, etc.); every other column is treated as a named layout, labelled using the file's own header spelling.
• Berkeley color palette — Berkeley Blue for selected seats, light gray for inactive, Rose Garden + slash for broken, California Gold for hover/focus and a "restricted use" marker dot. L label shown only for lefty-only seats (righty is the unlabelled default; broken/both-handed seats get no letter) to reduce visual noise.
• Edit mode — toggle seats individually to build a new layout; new layouts start with all seats selected; Select all / Clear / Invert / Deselect broken; right-click (or menu key) opens a per-seat attribute toggle menu; live-updating legend and counts.
• CSV export — writes the layout back out in the file's original column order plus a new, editable-named boolean column; verified to re-import cleanly.
• Legend covers seat state, markings, and every attribute/layout present in the uploaded file, with counts and descriptions, split by the layout/attribute distinction.
• Styling — reused existing MDL components (mdl-tabs, mdl-textfield, mdl-button, seat chart containers) to match app conventions; only seat colors depart from the app palette.
• Dev login — MOCK_CANVAS now defaults to true in DevelopmentConfig (env-overridable), explicitly false in StagingConfig (closing a hole where it previously inherited from env). Dev login page now lists seeded users with Canvas ID and enrollments for one-click login.
• Bug fix — replaced the header's expand_more Material Icons ligature with a CSS-drawn caret, since it rendered as literal text when the icon font was slow/blocked/unavailable.
• Tests — new unit test files for layout preview (test_layout_preview.py) and dev login gating/roster (test_dev_login.py).

Screenshots

• CSV upload/paste form
• Highlight mode
• Legend
• Right-click attribute menu
• Edit mode
• Dev login page

A wiki page draft describing the feature is also available: Seating-Layout-Preview.md (not pushed — the wiki repo isn't reachable from this environment; needs to be added manually alongside the screenshots above).

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Superconductor Ticket Implementation | App Preview | Guided Review