First-run onboarding: empty states, upload feedback & first-chat path (JOB-5)

[Pragadeesh122]

Summary

Tightens the first five minutes for a new user: create project → upload first doc → first grounded answer (JOB-5). Frontend-only, no backend changes.

First-run audit — friction points found

1. Empty project pushes generic prompts, not "upload a doc." A brand-new project opened straight into the general chat empty state ("Browse the web", "Query the database") — nothing pointed the user at uploading a document, which is the whole point of a project.
2. Silent upload failures. handleUploadFile swallowed errors to console.error; a bad type / too-large file / backend error left the spinner stopping with no explanation.
3. Wrong size limit in the UI. The dropzone said "Up to 25 MB" but the backend (api/projects.py) allows 100 MB.
4. Opaque processing. Documents showed a bare spinner with no "indexing / ready shortly" cue, and failed docs showed nothing.
5. Weak no-projects state. Just tiny grey "No projects yet" text; the only entry point was a 14px +.
6. No loading/error on project creation. Async create had no spinner and dropped errors to the console.
7. Generic suggestions even after upload. Once a doc was indexed, the empty state still offered generic prompts rather than "ask about your documents."

Changes

• ChatArea — project-aware empty state: when a project has no ready document, a hero upload dropzone (drag + click, wired to the real upload handler) with an indexing state and inline errors; once docs are ready, suggestions switch to grounded questions (summarize / ask about your documents).
• ProjectPage — pre-flight validation + inline upload-error state, threaded into both the sidebar and the chat hero.
• ProjectSidebar — corrected size copy (100 MB), inline upload-error banner, and a clearer per-document status line ("Indexing… ready to chat shortly" / failure reason).
• Sidebar — no-projects CTA ("Create your first project"); project creation now shows a spinner and surfaces errors inline.
• lib/upload.ts — single source of truth for supported types / size limit, kept in sync with the backend so client validation can't drift.

⚠️ Visual-quality decisions for CEO review (no designer on staff)

• New upload hero in the empty project view (dashed emerald dropzone, ~py-8). Matches existing emerald/zinc language but is a new focal element — worth an eyeball.
• No-projects sidebar CTA card replaces the one-line text.
• Copy choices (e.g. "Add a document to get started", "ready to chat shortly"). Happy to adjust tone.

Verification

• tsc --noEmit passes (exit 0). Production next build could not run in the isolated worktree (Turbopack rejects the cross-root node_modules symlink used to typecheck) — type/compile correctness is covered by tsc.
• Manual happy-path test plan (needs full stack — Postgres/Redis/Pinecone/MinIO):
  1. Sign in as a fresh user → /chat shows the "Create your first project" CTA.
  2. Create a project → spinner shows, redirect to the project; empty view shows the upload hero.
  3. Drag a PDF onto the hero → "Uploading…" → "Indexing…" → ready; suggestions switch to grounded questions.
  4. Try a .zip and a >100 MB file → friendly inline errors, no silent failure.
  5. Ask a grounded question → first cited answer.

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