test: Add and improve coverage thresholds across packages

Added coverage thresholds to all shared lib packages and increased
server thresholds to ensure better code quality and confidence.

Lib package thresholds:
- dependency-resolver: 90% stmts/lines, 85% branches, 100% funcs
- git-utils: 65% stmts/lines, 35% branches, 75% funcs
- utils: 15% stmts/lines/funcs, 25% branches (only error-handler tested)
- platform: 60% stmts/lines/branches, 40% funcs (only subprocess tested)

Server thresholds increased:
- From: 55% lines, 50% funcs, 50% branches, 55% stmts
- To: 60% lines, 75% funcs, 55% branches, 60% stmts
- Current actual: 64% lines, 78% funcs, 56% branches, 64% stmts

All tests passing with new thresholds. Lower thresholds on utils and
platform reflect that only some files have tests currently. These will
be increased as more tests are added.

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

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

apps/server/vitest.config.ts

@@ -17,12 +17,12 @@ export default defineConfig({
         "src/routes/**", // Routes are better tested with integration tests
       ],
       thresholds: {
-        // Thresholds lowered after moving lib files to shared packages
-        // TODO: Gradually increase as we add more tests
-        lines: 55,
-        functions: 50,
-        branches: 50,
-        statements: 55,
+        // Increased thresholds to ensure better code quality
+        // Current coverage: 64% stmts, 56% branches, 78% funcs, 64% lines
+        lines: 60,
+        functions: 75,
+        branches: 55,
+        statements: 60,
       },
     },
     include: ["tests/**/*.test.ts", "tests/**/*.spec.ts"],