Fix PDF font color not reflecting system settings via per-field merge

Root cause: resolveFontPrefsForUser() used `userRow ?? globalRow` whole-row
precedence. When an admin saved font settings with scope="global", only the
global row was updated. If the admin also had a user-scope row (created by
prior saves with the default scope="user"), ALL fields from the user-scope
row overrode the global row — including fontColor — causing the PDF to show
the old color even after changing global settings.

Schema change (executive-meetings.ts):
- Made fontFamily, fontSize, fontWeight, alignment, fontColor nullable.
  User-scope rows now store NULL for fields that inherit from global,
  and only store non-null values for fields the user explicitly overrode.

Backend fix (executive-meetings.ts):
- resolveFontPrefsForUser: per-field merge —
  user non-null → global non-null → schema default.
- PATCH handler for user-scope: after upsert, compares each field with the
  current global values. Fields matching global are set to NULL (= inherit).
  The post-nullification row is returned in the API response and audit log.
- No user-scope rows are deleted; scope isolation is preserved.

Frontend fix (executive-meetings.tsx):
- effectiveFont computed via per-field merge (u?.field ?? g?.field ?? default)
- FontSettingsResponse type updated for nullable fields (FontSettingsRow)
- Scope switching in FontSettingsSection loads the selected scope's values
  (global → globalFont ?? DEFAULT_FONT; user → effective font)
- globalFont prop threaded through SettingsSection → FontSettingsSection

Data migration: existing user-scope rows normalized via SQL — fields matching
global values set to NULL so per-field inheritance applies immediately.

Verified: TypeScript clean, e2e Playwright test passes, API tests confirm
per-field merge, nullification, and PDF color propagation.

lib/db/src/schema/executive-meetings.ts

@@ -270,16 +270,11 @@ export const executiveMeetingFontSettingsTable = pgTable(
     id: serial("id").primaryKey(),
     scope: varchar("scope", { length: 16 }).notNull().default("global"),
     userId: integer("user_id").references(() => usersTable.id, { onDelete: "cascade" }),
-    fontFamily: varchar("font_family", { length: 100 }).notNull().default("system"),
-    fontSize: integer("font_size").notNull().default(14),
-    fontWeight: varchar("font_weight", { length: 16 }).notNull().default("regular"),
-    alignment: varchar("alignment", { length: 16 }).notNull().default("start"),
-    // Hex color (#RRGGBB) applied to body cell text in both the on-screen
-    // schedule and the generated PDF. Default "#000000" preserves the
-    // historical black-text appearance for rows created before this
-    // column existed. Validated app-side by the regex in
-    // `fontSettingsSchema`.
-    fontColor: varchar("font_color", { length: 16 }).notNull().default("#000000"),
+    fontFamily: varchar("font_family", { length: 100 }).default("system"),
+    fontSize: integer("font_size").default(14),
+    fontWeight: varchar("font_weight", { length: 16 }).default("regular"),
+    alignment: varchar("alignment", { length: 16 }).default("start"),
+    fontColor: varchar("font_color", { length: 16 }).default("#000000"),
     // Object-storage path (`/objects/<id>`) of the brand logo embedded
     // in the top-left of the generated PDF header. NULL = no logo. Only
     // meaningful on the global-scope row (the per-user row ignores it).