Update specs to match implementation

Addresses spec drift items #3, 5, 6, 7, 8, 9, 10, 11, 12 from #147:

- transactional-emails: Resend → Nodemailer + SMTP
- infrastructure: CX21 → cx23
- secret-management: single secrets.env → split app/infra files
- brouter-integration: 5s failover delay → instant via clientID election
- brouter-integration: 2 profiles → 5 (trekking, fastbike, safety, shortest, car)
- observability: add version field to health response
- observability: add brouter_request_duration_seconds metric
- planner-session: remove 30-day max ceiling (not enforced)
- shared-packages: clarify map package scope vs planner-specific features

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

openspec/specs/transactional-emails/spec.md

@@ -5,7 +5,7 @@ The system SHALL provide a provider-agnostic email sending function that support
 
 #### Scenario: Send email in production
 - **WHEN** the system sends a transactional email in production
-- **THEN** the email is delivered via the configured provider (Resend) to the recipient
+- **THEN** the email is delivered via Nodemailer with SMTP (configured via `SMTP_URL` connection string and `SMTP_FROM` env var) to the recipient
 
 #### Scenario: Dev mode skips sending
 - **WHEN** the system sends a transactional email in development