Add schema compatibility probe to prevent silent migration failures (bd-ckvw)

- Implement comprehensive schema probe in sqlite.New() that verifies all
  expected tables and columns after migrations
- Add retry logic: if probe fails, retry migrations once
- Return clear fatal error with missing schema elements if probe still fails
- Enhance daemon version gating: refuse RPC if client has newer minor version
- Improve checkVersionMismatch messaging: verify schema before claiming upgrade
- Add schema compatibility check to bd doctor command
- Add comprehensive tests for schema probing

This prevents the silent migration failure bug where:
1. Migrations fail silently
2. Database queries fail with 'no such column' errors
3. Import logic misinterprets as 'not found' and tries INSERT
4. Results in cryptic UNIQUE constraint errors

Fixes #262

Amp-Thread-ID: https://ampcode.com/threads/T-0d7ae2c0-9f12-4f9b-85d1-1291488af150
Co-authored-by: Amp <amp@ampcode.com>

internal/rpc/version_test.go

@@ -323,7 +323,7 @@ func TestVersionCheckMessage(t *testing.T) {
 			serverVersion: testVersion100,
 			clientVersion: "1.1.0",
 			expectError:   true,
-			errorContains: "daemon 1.0.0 is older than client 1.1.0",
+			errorContains: "client v1.1.0 requires daemon upgrade",
 		},
 		{
 			name:          "Compatible versions",