Add Iron Coast II Black Tide eight-mission campaign

mods/iron_coast_depth_charge/README.md

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+# Depth Charge 1.0.0
+
+Enable **Depth Charge** in Mods, apply at the main menu, then buy it in the shop
+for **525,000 credits**. It is an independent API 1 mod without dependencies or
+overrides. Maximum one; resale returns 262,500 credits. It occupies a normal
+inventory slot and preserves other equipment.
+
+This is a **selectable, reusable ground/naval special weapon**. Choose it in
+Inventory or with Alt/Shift, then hold Ctrl to launch. Space remains the owned
+mega-bomb control. It does not consume charges or auto-attack merely because it
+is equipped. Always-equipped forward guns remain available alongside it.
+
+The native straight projectile travels six logical pixels per simulation tick.
+A real ground-enemy collision deals 72 primary damage and starts one local
+ground-blast effect. At most three other living ground enemies can receive
+collateral damage: 36 damage within 16 pixels of the primary enemy's center,
+or 20 damage between 16 and 36 pixels inclusive. The closest neighbors are
+selected first, with stable entity order breaking ties. Aircraft, offscreen
+enemies, repeated targets and centers outside that radius are excluded. If the
+primary target dies, its contact still triggers the local blast correctly.
+
+The deliberate 48-tick cooldown is about 2.06 seconds at 70/3 Hz. The charge does
+not home or detonate automatically in empty space. Slow travel makes moving
+ground targets an aiming challenge; there is no screen-wide damage command.
+Destructible terrain receives native primary damage, but cannot trigger scripted
+collateral because the public snapshot contains enemies rather than terrain
+cells. Enemy contacts emit impact audio; a miss produces only the launch sound
+and projectile. The normal native terrain destruction effects remain available.
+
+SD equipment/projectile canvases are 16×16 and 8×12; detailed HD variants are
+64×64 and 32×48. Options selects SD or HD artwork without changing logical
+placement or damage. Both are single aligned frames with transparent margins.
+[Artwork provenance](art-provenance.json) records unchanged generated masters,
+prompts, final PNG hashes and the Rust preparation recipe. All new images, WAVs,
+source masters and recipes are included; decoded original style references are
+kept outside the mod.
+
+`python3 generate_audio.py` reproduces the mechanical launch and low naval impact
+from deterministic synthesis without external recordings. `prepare_art.rs`
+rebuilds SD/HD fitting from the included source masters. The companion Railburst
+package's [review helper](../iron_coast_railburst/validation/review.py) is a developer
+tool for both packages and is not a gameplay dependency.
+
+From the RustRaptor directory:
+
+```sh
+cargo test --locked --no-default-features --test iron_coast_stage2_weapons
+cargo run --locked --no-default-features -- --data data --mods mods \
+  --validate-mods iron_coast_depth_charge
+IRON_COAST_STAGE2_BALANCE_REPORT=/tmp/stage2-balance.json \
+  cargo test --locked --no-default-features --test iron_coast_stage2_weapons \
+  real_catalog_700_tick_balance_and_coexistence_report -- --ignored --nocapture
+```
+
+[validation/balance.json](validation/balance.json) records the actual controlled
+700-tick damage observations supporting this price and role. Portable checks
+cover ground filtering, inner/outer falloff, the finite neighbor cap, misses,
+kills, cooldown, independent activation, coexistence, half-price resale, full
+inventory preservation, deterministic state/RNG continuation and whole-tick
+rollback. [validation/review.json](validation/review.json) distinguishes public
+decoder/blitter/mixer captures from live desktop review. Read the [API](../../docs/modding-api.md)
+for save pins and script execution limits.