[P9-2] DB schema: add title to plots + create comments table

[realproject7]

Changes

1. Add title column to plots table

ALTER TABLE plots ADD COLUMN title TEXT DEFAULT '';

• Default empty string for backward compatibility with existing plots
• Update Supabase TypeScript types in lib/supabase.ts
• Update plot indexer (/api/index/plot/route.ts) to extract title from PlotChained event

2. Create comments table

CREATE TABLE comments (
  id SERIAL PRIMARY KEY,
  storyline_id INTEGER NOT NULL REFERENCES storylines(storyline_id),
  plot_index INTEGER NOT NULL,  -- 0 = genesis, 1+ = chapter
  commenter_address TEXT NOT NULL,
  content TEXT NOT NULL,
  created_at TIMESTAMPTZ DEFAULT NOW(),
  hidden BOOLEAN DEFAULT FALSE
);

CREATE INDEX idx_comments_storyline_plot ON comments(storyline_id, plot_index);
CREATE INDEX idx_comments_commenter ON comments(commenter_address);

• plot_index = 0 for comments on genesis
• plot_index = N for comments on chapter N
• hidden for moderation support
• Update Supabase TypeScript types

3. Create comments API routes

• GET /api/comments?storylineId=X&plotIndex=Y&page=1&limit=20 — paginated fetch
• POST /api/comments — create comment (requires wallet signature)

Blocked by

#184 (contract must be deployed first for title in events)

Part of

Phase 9 Epic (#183)