refactor: Remove redundant doc comments throughout codebase

Removes module-level doc comments (//! lines) and excessive inline doc
comments that were duplicating information already evident from:
- Function/struct names (self-documenting code)
- Type signatures (the what is clear from types)
- Implementation context (the how is clear from code)

Affected modules:
- cli/* - Removed command descriptions duplicating clap help text
- core/* - Removed module headers and obvious function docs
- documents/* - Removed extractor/regenerator/truncation docs
- embedding/* - Removed pipeline and chunking docs
- gitlab/* - Removed client and transformer docs (kept type definitions)
- ingestion/* - Removed orchestrator and ingestion docs
- search/* - Removed FTS and vector search docs

Philosophy: Code should be self-documenting. Comments should explain
"why" (business decisions, non-obvious constraints) not "what" (which
the code itself shows). This change reduces noise and maintenance burden
while keeping the codebase just as understandable.

Retains comments for:
- Non-obvious business logic
- Important safety invariants
- Complex algorithm explanations
- Public API boundaries where generated docs matter

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/gitlab/transformers/merge_request.rs

@@ -1,9 +1,6 @@
-//! Merge request transformer: converts GitLabMergeRequest to local schema.
-
 use crate::core::time::{iso_to_ms_opt_strict, iso_to_ms_strict, now_ms};
 use crate::gitlab::types::GitLabMergeRequest;
 
-/// Local schema representation of a merge request row.
 #[derive(Debug, Clone)]
 pub struct NormalizedMergeRequest {
     pub gitlab_id: i64,
@@ -21,15 +18,14 @@ pub struct NormalizedMergeRequest {
     pub references_full: Option<String>,
     pub detailed_merge_status: Option<String>,
     pub merge_user_username: Option<String>,
-    pub created_at: i64,        // ms epoch UTC
-    pub updated_at: i64,        // ms epoch UTC
-    pub merged_at: Option<i64>, // ms epoch UTC
-    pub closed_at: Option<i64>, // ms epoch UTC
-    pub last_seen_at: i64,      // ms epoch UTC
+    pub created_at: i64,
+    pub updated_at: i64,
+    pub merged_at: Option<i64>,
+    pub closed_at: Option<i64>,
+    pub last_seen_at: i64,
     pub web_url: String,
 }
 
-/// Merge request bundled with extracted metadata.
 #[derive(Debug, Clone)]
 pub struct MergeRequestWithMetadata {
     pub merge_request: NormalizedMergeRequest,
@@ -38,61 +34,43 @@ pub struct MergeRequestWithMetadata {
     pub reviewer_usernames: Vec<String>,
 }
 
-/// Transform a GitLab merge request into local schema format.
-///
-/// # Arguments
-/// * `gitlab_mr` - The GitLab MR API response
-/// * `local_project_id` - The local database project ID (not GitLab's project_id)
-///
-/// # Returns
-/// * `Ok(MergeRequestWithMetadata)` - Transformed MR with extracted metadata
-/// * `Err(String)` - Error message if transformation fails (e.g., invalid timestamps)
 pub fn transform_merge_request(
     gitlab_mr: &GitLabMergeRequest,
     local_project_id: i64,
 ) -> Result<MergeRequestWithMetadata, String> {
-    // Parse required timestamps
     let created_at = iso_to_ms_strict(&gitlab_mr.created_at)?;
     let updated_at = iso_to_ms_strict(&gitlab_mr.updated_at)?;
 
-    // Parse optional timestamps
     let merged_at = iso_to_ms_opt_strict(&gitlab_mr.merged_at)?;
     let closed_at = iso_to_ms_opt_strict(&gitlab_mr.closed_at)?;
 
-    // Draft: prefer draft, fallback to work_in_progress
     let is_draft = gitlab_mr.draft || gitlab_mr.work_in_progress;
 
-    // Merge status: prefer detailed_merge_status over legacy
     let detailed_merge_status = gitlab_mr
         .detailed_merge_status
         .clone()
         .or_else(|| gitlab_mr.merge_status_legacy.clone());
 
-    // Merge user: prefer merge_user over merged_by
     let merge_user_username = gitlab_mr
         .merge_user
         .as_ref()
         .map(|u| u.username.clone())
         .or_else(|| gitlab_mr.merged_by.as_ref().map(|u| u.username.clone()));
 
-    // References extraction
     let (references_short, references_full) = gitlab_mr
         .references
         .as_ref()
         .map(|r| (Some(r.short.clone()), Some(r.full.clone())))
         .unwrap_or((None, None));
 
-    // Head SHA
     let head_sha = gitlab_mr.sha.clone();
 
-    // Extract assignee usernames
     let assignee_usernames: Vec<String> = gitlab_mr
         .assignees
         .iter()
         .map(|a| a.username.clone())
         .collect();
 
-    // Extract reviewer usernames
     let reviewer_usernames: Vec<String> = gitlab_mr
         .reviewers
         .iter()