refactor(core): Rename GiError to LoreError and add search infrastructure

Mechanical rename of GiError -> LoreError across the core module to
match the project's rebranding from gitlab-inbox to gitlore/lore.
Updates the error enum name, all From impls, and the Result type alias.

Additionally introduces:

- New error variants for embedding pipeline: OllamaUnavailable,
  OllamaModelNotFound, EmbeddingFailed, EmbeddingsNotBuilt. Each
  includes actionable suggestions (e.g., "ollama serve", "ollama pull
  nomic-embed-text") to guide users through recovery.

- New error codes 14-16 for programmatic handling of Ollama failures.

- Savepoint-based migration execution in db.rs: each migration now
  runs inside a SQLite SAVEPOINT so a failed migration rolls back
  cleanly without corrupting the schema_version tracking. Previously
  a partial migration could leave the database in an inconsistent
  state.

- core::backoff module: exponential backoff with jitter utility for
  retry loops in the embedding pipeline and discussion queues.

- core::project module: helper for resolving project IDs and paths
  from the local database, used by the document regenerator and
  search filters.

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

src/core/config.rs

@@ -6,7 +6,7 @@ use serde::Deserialize;
 use std::fs;
 use std::path::Path;
 
-use super::error::{GiError, Result};
+use super::error::{LoreError, Result};
 use super::paths::get_config_path;
 
 /// GitLab connection settings.
@@ -130,7 +130,7 @@ impl Config {
         let config_path = get_config_path(cli_override);
 
         if !config_path.exists() {
-            return Err(GiError::ConfigNotFound {
+            return Err(LoreError::ConfigNotFound {
                 path: config_path.display().to_string(),
             });
         }
@@ -140,25 +140,25 @@ impl Config {
 
     /// Load configuration from a specific path.
     pub fn load_from_path(path: &Path) -> Result<Self> {
-        let content = fs::read_to_string(path).map_err(|e| GiError::ConfigInvalid {
+        let content = fs::read_to_string(path).map_err(|e| LoreError::ConfigInvalid {
             details: format!("Failed to read config file: {e}"),
         })?;
 
         let config: Config =
-            serde_json::from_str(&content).map_err(|e| GiError::ConfigInvalid {
+            serde_json::from_str(&content).map_err(|e| LoreError::ConfigInvalid {
                 details: format!("Invalid JSON: {e}"),
             })?;
 
         // Validate required fields
         if config.projects.is_empty() {
-            return Err(GiError::ConfigInvalid {
+            return Err(LoreError::ConfigInvalid {
                 details: "At least one project is required".to_string(),
             });
         }
 
         for project in &config.projects {
             if project.path.is_empty() {
-                return Err(GiError::ConfigInvalid {
+                return Err(LoreError::ConfigInvalid {
                     details: "Project path cannot be empty".to_string(),
                 });
             }
@@ -166,7 +166,7 @@ impl Config {
 
         // Validate URL format
         if url::Url::parse(&config.gitlab.base_url).is_err() {
-            return Err(GiError::ConfigInvalid {
+            return Err(LoreError::ConfigInvalid {
                 details: format!("Invalid GitLab URL: {}", config.gitlab.base_url),
             });
         }