Add battery dispatch implementation and Gitea CI pipeline

Implements the package from PLAN.md: config/data loading, the LP-first
MILP-fallback rolling-horizon optimiser, battery degradation tracking,
independent schedule validation, metrics, plots and the CLI, plus the
matching test suite. Adds a Gitea Actions workflow (lint + tests) that
posts a pass/fail notification to ntfy on every run, and a .gitignore
for build/cache artefacts that had been tracked by mistake.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/battery_dispatch/markets.py

@@ -0,0 +1,55 @@
+"""Market definitions.
+
+Both markets are expressed on the common half-hourly grid. A market whose
+trading block is longer than a half-hour (Market 2, hourly) is described by
+``block_half_hours``; the optimiser creates one decision variable per *block*
+and references it from every half-hour inside that block, so the commitment
+rule cannot be violated by construction.
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+
+import numpy as np
+
+MARKET_1 = "market_1"
+MARKET_2 = "market_2"
+
+
+@dataclass(frozen=True)
+class Market:
+    """A market the battery can trade in.
+
+    Attributes:
+        name: Identifier used in output column names.
+        block_half_hours: Number of half-hours a single commitment must span.
+        prices: One price per half-hour, broadcast from the block price.
+    """
+
+    name: str
+    block_half_hours: int
+    prices: np.ndarray
+
+    def __post_init__(self) -> None:
+        if self.block_half_hours < 1:
+            raise ValueError("block_half_hours must be >= 1")
+        if self.prices.ndim != 1:
+            raise ValueError("prices must be one-dimensional")
+
+    def block_of(self, half_hour: int) -> int:
+        """Index of the trading block containing ``half_hour``."""
+        return half_hour // self.block_half_hours
+
+    def slice(self, start: int, stop: int) -> "Market":
+        """A view of this market over half-hours ``[start, stop)``.
+
+        ``start`` must fall on a block boundary, otherwise the window would cut
+        a trading block in half and the commitment rule would be meaningless.
+        """
+        if start % self.block_half_hours:
+            raise ValueError(
+                f"{self.name}: window start {start} is not aligned to a "
+                f"{self.block_half_hours}-half-hour block boundary"
+            )
+        return Market(self.name, self.block_half_hours, self.prices[start:stop])