docs(openspec): archive completed changes and sync main specs

Archive three completed changes to archive/:
- api-resource-standard (70 tasks, 14 resource classes)
- capacity-expert-mode (68 tasks, expert mode planning grid)
- enhanced-allocation (62 tasks, planning fidelity + reporting)

Sync all delta specs to main specs/:
- api-resource-standard: API response standardization
- capacity-expert-mode: Expert mode toggle, grid, KPIs, batch API
- resource-allocation: Month execution comparison, bulk, untracked
- untracked-allocation: Null team member support
- allocation-indicators: Variance indicators (red/amber/neutral)
- monthly-budget: Explicit project-month planning

All changes verified and tested (157 tests passing).

openspec/changes/archive/2026-03-08-enhanced-allocation/specs/monthly-budget/spec.md

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+# Project-Month Plan Specification
+
+## Overview
+
+This capability defines explicit manager-entered monthly planning per project.
+It replaces derived monthly budget assumptions and becomes the planning source of truth for allocation variance.
+
+## ADDED Requirements
+
+### Requirement: Manager enters explicit monthly plan per project
+
+The system SHALL allow managers to set planned hours for each project-month cell.
+
+#### Scenario: Set monthly plan across multiple months
+- **GIVEN** project `PROJ-001` has `approved_estimate = 3000`
+- **WHEN** manager sets Jan=1200, Feb=1400, Mar=400
+- **THEN** the system stores those exact values
+- **AND** no derived monthly average is applied
+
+#### Scenario: Edit monthly plan cell inline
+- **GIVEN** a month-plan grid cell contains 1200
+- **WHEN** manager edits the cell to 1100 and commits
+- **THEN** the system persists 1100
+- **AND** reconciliation status recalculates immediately
+
+### Requirement: Reconcile month-plan sum against lifecycle approved estimate
+
+The system SHALL compute reconciliation status per project based on:
+`sum(non-null monthly planned hours)` vs `approved_estimate`.
+
+#### Scenario: OVER reconciliation
+- **GIVEN** `approved_estimate = 3000`
+- **AND** month-plan sum is 3200
+- **THEN** status is `OVER`
+
+#### Scenario: UNDER reconciliation
+- **GIVEN** `approved_estimate = 3000`
+- **AND** month-plan sum is 2800
+- **THEN** status is `UNDER`
+
+#### Scenario: MATCH reconciliation
+- **GIVEN** `approved_estimate = 3000`
+- **AND** month-plan sum is 3000
+- **THEN** status is `MATCH`
+
+### Requirement: Preserve blank month semantics
+
+The planning grid SHALL keep unset months visually blank and semantically distinct from explicit zero.
+
+#### Scenario: Blank remains blank
+- **GIVEN** no plan exists for April
+- **WHEN** manager views planning grid
+- **THEN** April cell is blank (no `0` shown)
+
+#### Scenario: Clear cell sets blank semantics
+- **GIVEN** a month cell has planned value
+- **WHEN** manager clears the cell and commits
+- **THEN** the month is stored as blank/unset semantics
+- **AND** planning UI displays blank
+
+### Requirement: Allocation variance uses blank plan as zero
+
+For allocation variance computation only, missing month plan SHALL be treated as planned `0`.
+
+#### Scenario: Allocate against blank plan month
+- **GIVEN** no plan is set for selected month
+- **AND** project allocations total 40h
+- **WHEN** variance is computed
+- **THEN** planned value used is 0
+- **AND** row variance is +40
+- **AND** allocation operation remains allowed
+
+### Requirement: Grid-first planning interaction
+
+Project-month planning SHALL be managed in a grid-first interface.
+
+#### Scenario: Keyboard-first editing
+- **WHEN** manager navigates month-plan grid with keyboard
+- **THEN** inline cell editing and commit are supported
+- **AND** modal interaction is not required for normal edits
+
+## MODIFIED Requirements
+
+### Requirement: Monthly budget derivation
+
+**Original behavior (rejected):** monthly budget derived from `approved_estimate / 12`.
+
+**Updated behavior:** monthly plan values are explicit manager-entered project-month values; no derivation formula is used for planning behavior.