feat: add city-wide troop training pipelines

[prayujt]

Outcome

Moves troop training from independent barracks queues to one durable FIFO pipeline per city. Completed barracks process that pipeline in parallel and spawn each finished army at the barracks lane that trained it.

It also makes active combat readable in real time and introduces durable, player-editable army names.

What changed

• Makes the city actor authoritative for queue ownership, resource reservation, FIFO assignment, completion, and cancellation.
• Reserves gold and population when an order enters the queue.
• Allows only unstarted orders to be cancelled, with a full refund of their recorded gold and population costs.
• Gives every completed barracks one active lane; idle lanes atomically claim the oldest waiting batch.
• Uses barracks level as a lane-speed modifier: 1.0x at level 1, then +0.2x per level through 2.8x at level 10.
• Blocks barracks upgrade/demolition only while that specific barracks has active work.
• Migrates durable orders to city ownership with optional barracks assignment and database constraints for one active order per barracks.
• Changes training RPCs to use city IDs, adds CancelTrainingOrder, exposes authoritative order costs, and exposes barracks training speed through game config.
• Updates the development helper and backend architecture/API documentation.

Combat visibility and balance

• Exposes cumulative and latest-round troop, militia, and civilian casualties for both sides while a battle is active.
• Includes completed-round counts and live friendly starting/surviving strength.
• Keeps opposing starting strength, surviving strength, militia totals, and combat power concealed unless existing disclosure rules allow them.
• Applies the same casualty disclosure to durable mailbox reports so losses remain reviewable offline.
• Uses a 1.0 military casualty multiplier while retaining the five-second battle cadence.
• Derives siege civilian collateral from actual army and militia losses at 0.15 civilian casualties per military casualty, with fractional carry.
• Preserves at least 30% of the settlement normal 55% core-civilian allocation.
• Keeps field battles free of civilian casualties.

Army names

• Persists an army name on every army and snapshots it into battle reports.
• Defaults generated armies to Army plus the first eight characters of their UUID.
• Adds an owner-only RenameArmy RPC.
• Trims names, rejects blanks/control characters, and limits them to 32 characters.
• Enforces case-insensitive uniqueness per owner in PostgreSQL and maps collisions to AlreadyExists.
• Streams successful renames immediately.

Compatibility

This intentionally changes unreleased proto and persistence contracts. The matching UI/client work is in web PR #19.

Verification

• go test ./...
• go build ./...
• go vet ./...
• buf lint
• goose migration validation
• clean migration up → down-to-zero → up round trip
• case-insensitive duplicate-name constraint check