feat: Implement junior fees dashboard and reconciliation

- Add dual-sheet architecture to pull attendance from both adult and junior spreadsheets.
- Introduce parsing rules to isolate juniors (e.g. above '# Treneri', tier 'J').
- Add new endpoints `/fees-juniors` and `/reconcile-juniors` to track junior attendances and match bank payments.
- Display granular attendance components showing adult vs. junior practices.
- Add fee rule configuration supporting custom pricing exceptions for specific months (e.g. Sep 2025) and merging billing periods.
- Add `make sync-2025` target to the Makefile for convenience.
- Document junior fees implementation logic and rules in prompts/outcomes.

Co-authored-by: Antigravity <antigravity@google.com>

prompts/outcomes/2026-03-09-junior-fees.md

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+# Junior Fees Implementation Summary
+
+Based on the recent updates, we have introduced a dedicated system for tracking, displaying, and reconciling junior team attendances and payments. 
+
+## 1. Implemented Features
+- **Dual-Sheet Architecture:** The system now pulls attendance from two separate Google Sheet tabs—one for adult practices and another for junior practices.
+- **New Views:** 
+  - `/fees-juniors`: A dedicated dashboard showing junior attendances and calculated fees.
+  - `/reconcile-juniors`: A dedicated page matching Fio bank transactions against expected junior fees.
+- **Granular Attendance Display:** The UI clearly separates and tallies adult (`A`) and junior (`J`) practice counts for each member (e.g., `4 (2A+2J)` or `2 (J)`).
+
+## 2. Membership Rules
+- **Identification:** A member is processed as a junior if they appear in the *Junior Sheet*, UNLESS:
+  - They are listed below the separator line `# Treneri` (or `# Trenéři`).
+  - Their tier is explicitly marked as `X`.
+- **Adult Sheet Fallback:** Members from the Adult Sheet whose tier is marked as `J` are also tracked as juniors.
+- **Merging Identities:** If a member has the identical name in both the Adult Sheet and the Junior Sheet, their attendance records are merged together into a single profile.
+
+## 3. Fee Calculation Rules
+The base fee calculation for juniors relies on the total combined attendance across both adult and junior practices for a given month:
+- **0 attendances:** 0 CZK
+- **Exactly 1 attendance:** `?` (Flags the month for manual review/decision)
+- **2 or more attendances:** 500 CZK (Default base rate)
+
+## 4. Exceptions & Overrides
+We have hardcoded specific timeline and pricing exceptions directly into the logic:
+
+- **Modified Monthly Rates:** 
+  - **September 2025** (`2025-09`) is explicitly configured to have a fee of **250 CZK** for 2+ attendances instead of the default 500 CZK.
+
+- **Merged Billing Months:** 
+  To handle holidays and off-seasons, certain subsequent months are merged and billed as a single period. Their attendances are summed up before the fee rule is applied. The current active merges are:
+  - **December 2025** is merged into **January 2026**
+  - **September 2025** is merged into **October 2025**