style(db): address two informational nits from reviewer pass on 69f7001

Both items came back APPROVE-with-info on the prior review and are
pure cleanup — no behavior change, no API surface change.

## #1 — RHEL/Fedora step in WASM_FALLBACK_FIX_RECIPE constant

The constant in `src/db/sqlite-adapter.ts` is documented as the
"single source of truth" for the fix recipe shown in the MCP
`Backend:` line, but it only listed macOS + Debian/Ubuntu paths. The
multi-line `buildWasmFallbackBanner` and the README both already
include the `yum groupinstall "Development Tools"` step for
RHEL/Fedora; the constant was the lone surface missing it. Now
appended so MCP-displayed guidance matches the other two surfaces
on every supported platform.

## #2 — hoist inline `import('./db').SqliteBackend` to top-level

`CodeGraph.getBackend()` was the only method in `src/index.ts` using
the inline-import type form. Adding `SqliteBackend` to the existing
`import { DatabaseConnection, getDatabasePath } from './db'` keeps
the file consistent. No circular-import risk since `./db` already
re-exports the type from `./db/sqlite-adapter`.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: andreinknv

src/db/sqlite-adapter.ts

@@ -28,8 +28,9 @@ export type SqliteBackend = 'native' | 'wasm';
  * formatter so the recipe can't drift between surfaces.
  */
 export const WASM_FALLBACK_FIX_RECIPE =
-  '`xcode-select --install` (macOS) or `apt install build-essential` (Debian/Ubuntu), ' +
-  'then `npm rebuild better-sqlite3`, or `npm install better-sqlite3 --save` to force-include it.';
+  '`xcode-select --install` (macOS), `apt install build-essential` (Debian/Ubuntu), ' +
+  'or `yum groupinstall "Development Tools"` (RHEL/Fedora), then `npm rebuild better-sqlite3`, ' +
+  'or `npm install better-sqlite3 --save` to force-include it.';
 
 /**
  * Multi-line banner shown to stderr when `createDatabase` falls back to

src/index.ts

@@ -23,7 +23,7 @@ import {
   BuildContextOptions,
   FindRelevantContextOptions,
 } from './types';
-import { DatabaseConnection, getDatabasePath } from './db';
+import { DatabaseConnection, SqliteBackend, getDatabasePath } from './db';
 import { QueryBuilder } from './db/queries';
 import { loadConfig, saveConfig, createDefaultConfig } from './config';
 import {
@@ -1592,7 +1592,7 @@ export class CodeGraph {
    * right backend even if other projects in the same process happen
    * to be on a different one.
    */
-  getBackend(): import('./db').SqliteBackend {
+  getBackend(): SqliteBackend {
     return this.db.getBackend();
   }