feat(life): add reactions to life posts

Support 'like', 'helpful', 'fun', and 'thanks' reactions.
Add API endpoints and database schema for post reactions.
Update UI with reaction picker and summary counts.

backend/db/schema.sql

@@ -152,6 +152,18 @@ CREATE INDEX IF NOT EXISTS life_post_comments_post_idx
 CREATE INDEX IF NOT EXISTS life_post_comments_parent_idx
   ON life_post_comments(parent_comment_id, created_at, id);
 
+CREATE TABLE IF NOT EXISTS life_post_reactions (
+  post_id integer NOT NULL REFERENCES life_posts(id) ON DELETE CASCADE,
+  user_id integer NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+  reaction_type text NOT NULL CHECK (reaction_type IN ('like', 'helpful', 'fun', 'thanks')),
+  created_at timestamptz NOT NULL DEFAULT now(),
+  updated_at timestamptz NOT NULL DEFAULT now(),
+  PRIMARY KEY (post_id, user_id)
+);
+
+CREATE INDEX IF NOT EXISTS life_post_reactions_post_idx
+  ON life_post_reactions(post_id, reaction_type);
+
 CREATE TABLE IF NOT EXISTS skills (
   id integer GENERATED BY DEFAULT AS IDENTITY PRIMARY KEY,
   name text NOT NULL UNIQUE,