refactor: rename skipStarredIssues to starredCodeOnly

The previous name 'skipStarredIssues' was misleading as it now skips ALL
metadata (not just issues) for starred repositories. The new name
'starredCodeOnly' better reflects the actual behavior - mirroring only
source code for starred repos.

Changes:
- Renamed skipStarredIssues → starredCodeOnly in all files
- Updated UI label from "Don't fetch issues" to "Code-only mode"
- Updated description to clarify it skips ALL metadata types:
  issues, PRs, labels, milestones, wiki, and releases
- Updated database schema, types, config mapper, and all components
- Updated Helm charts, CI configs, and documentation

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/lib/db/schema.ts

@@ -27,7 +27,7 @@ export const githubConfigSchema = z.object({
   starredReposOrg: z.string().optional(),
   mirrorStrategy: z.enum(["preserve", "single-org", "flat-user", "mixed"]).default("preserve"),
   defaultOrg: z.string().optional(),
-  skipStarredIssues: z.boolean().default(false),
+  starredCodeOnly: z.boolean().default(false),
   starredDuplicateStrategy: z.enum(["suffix", "prefix", "owner-org"]).default("suffix").optional(),
 });