fix(capacity): stabilize PTO flows and calendar consistency

Make PTO creation immediately approved, add PTO deletion, and ensure cache invalidation updates individual/team/revenue capacity consistently.

Harden holiday duplicate handling (422), support PTO-day availability overrides without disabling edits, and align tests plus OpenSpec artifacts with the new behavior.

openspec/changes/headroom-foundation/specs/capacity-planning/spec.md

@@ -87,13 +87,23 @@ The system SHALL allow team members to request PTO which reduces their individua
 
 #### Scenario: Submit PTO request
 - **WHEN** a team member submits PTO for February 10-12, 2026
-- **THEN** the system creates a PTO record with start date, end date, and status "pending"
+- **THEN** the system creates a PTO record with start date, end date, and status "approved"
 
 #### Scenario: Approve PTO request
 - **WHEN** a manager approves a PTO request
 - **THEN** the system updates the PTO status to "approved"
 - **AND** the system automatically reduces the team member's capacity for those dates to 0
 
+#### Scenario: Delete PTO request
+- **WHEN** a manager deletes an existing PTO request
+- **THEN** the PTO record is removed
+- **AND** individual, team, and revenue capacity caches for affected months are refreshed
+
 #### Scenario: PTO affects capacity calculation
 - **WHEN** calculating capacity for a team member with approved PTO for 3 days
 - **THEN** the system excludes those 3 days from the capacity calculation
+
+#### Scenario: Override PTO day availability
+- **WHEN** a PTO day is manually set to half day availability (0.5)
+- **THEN** the system keeps the PTO marker for that date
+- **AND** the capacity calculation uses the explicit availability override instead of forcing 0