Monorepo: consolidate 7 repos into one

Combines shared, blog, market, cart, events, federation, and account
into a single repository. Eliminates submodule sync, sibling model
copying at build time, and per-app CI orchestration.

Changes:
- Remove per-app .git, .gitmodules, .gitea, submodule shared/ dirs
- Remove stale sibling model copies from each app
- Update all 6 Dockerfiles for monorepo build context (root = .)
- Add build directives to docker-compose.yml
- Add single .gitea/workflows/ci.yml with change detection
- Add .dockerignore for monorepo build context
- Create __init__.py for federation and account (cross-app imports)

shared/utils/calendar_helpers.py

@@ -0,0 +1,54 @@
+"""Pure calendar utility functions (no ORM dependencies).
+
+Extracted from events/bp/calendar/services/calendar_view.py so that
+blog admin (and any other app) can use them without cross-app imports.
+"""
+from __future__ import annotations
+
+import calendar as pycalendar
+from datetime import datetime, timezone
+
+from quart import request
+
+
+def parse_int_arg(name: str, default: int | None = None) -> int | None:
+    """Parse an integer query parameter from the request."""
+    val = request.args.get(name, "").strip()
+    if not val:
+        return default
+    try:
+        return int(val)
+    except ValueError:
+        return default
+
+
+def add_months(year: int, month: int, delta: int) -> tuple[int, int]:
+    """Add (or subtract) months to a given year/month, handling year overflow."""
+    new_month = month + delta
+    new_year = year + (new_month - 1) // 12
+    new_month = ((new_month - 1) % 12) + 1
+    return new_year, new_month
+
+
+def build_calendar_weeks(year: int, month: int) -> list[list[dict]]:
+    """Build a calendar grid for the given year and month.
+
+    Returns a list of weeks, where each week is a list of 7 day dicts.
+    """
+    today = datetime.now(timezone.utc).date()
+    cal = pycalendar.Calendar(firstweekday=0)  # 0 = Monday
+    weeks: list[list[dict]] = []
+
+    for week in cal.monthdatescalendar(year, month):
+        week_days = []
+        for d in week:
+            week_days.append(
+                {
+                    "date": d,
+                    "in_month": (d.month == month),
+                    "is_today": (d == today),
+                }
+            )
+        weeks.append(week_days)
+
+    return weeks