fix(ingestion): label upsert reliability, init idempotency, and sync health

Label upsert (issues + merge_requests): Replace INSERT ... ON CONFLICT DO
UPDATE RETURNING with INSERT OR IGNORE + SELECT. The prior RETURNING-based
approach relied on last_insert_rowid() matching the returned id, which is
not guaranteed when ON CONFLICT triggers an update (SQLite may return 0).
The new two-step approach is unambiguous and correctly tracks created_count.

Init: Add ON CONFLICT(gitlab_project_id) DO UPDATE to the project insert
so re-running `lore init` updates path/branch/url instead of failing with
a unique constraint violation.

MR discussions sync: Reset discussions_sync_attempts to 0 when clearing a
sync health error, so previously-failed MRs get a fresh retry budget after
successful sync.

Count: format_number now handles negative numbers correctly by extracting
the sign before inserting thousand-separators.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/cli/commands/init.rs

@@ -133,7 +133,11 @@ pub async fn run_init(inputs: InitInputs, options: InitOptions) -> Result<InitRe
     for (_, gitlab_project) in &validated_projects {
         conn.execute(
             "INSERT INTO projects (gitlab_project_id, path_with_namespace, default_branch, web_url)
-             VALUES (?, ?, ?, ?)",
+             VALUES (?, ?, ?, ?)
+             ON CONFLICT(gitlab_project_id) DO UPDATE SET
+               path_with_namespace = excluded.path_with_namespace,
+               default_branch = excluded.default_branch,
+               web_url = excluded.web_url",
             (
                 gitlab_project.id,
                 &gitlab_project.path_with_namespace,