fix(channelserver): post-RC1 stabilization sprint

Fix rasta_id=0 overwriting NULL in SaveMercenary, which prevented
game state saving for characters without a mercenary (#163).

Also includes:
- CHANGELOG updated with all 10 post-RC1 commits
- Setup wizard fmt.Printf replaced with zap structured logging
- technical-debt.md updated with 6 newly completed items
- Scenario binary format documented (docs/scenario-format.md)
- Tests: alliance nil-guard (#171), handler dispatch table,
  migrations (sorted/SQL/baseline), setup wizard (10 tests),
  protbot protocol sign/entrance/channel (23 tests)

docs/scenario-format.md

@@ -0,0 +1,56 @@
+# Scenario Binary Format
+
+> Reference: `network/mhfpacket/msg_sys_get_file.go`, issue [#172](https://github.com/Mezeporta/Erupe/issues/172)
+
+## Overview
+
+Scenario files are binary blobs served by `MSG_SYS_GET_FILE` when `IsScenario` is true. They contain quest descriptions, NPC dialog, episode listings, and menu options for the game's scenario/story system.
+
+## Request Format
+
+When `IsScenario == true`, the client sends a `scenarioFileIdentifier`:
+
+| Offset | Type   | Field       | Description |
+|--------|--------|-------------|-------------|
+| 0      | uint8  | CategoryID  | Scenario category |
+| 1      | uint32 | MainID      | Main scenario identifier |
+| 5      | uint8  | ChapterID   | Chapter within the scenario |
+| 6      | uint8  | Flags       | Bit flags selecting chunk types (see below) |
+
+## Flags (Chunk Type Selection)
+
+The `Flags` byte is a bitmask that selects which chunk types the client requests:
+
+| Bit  | Value | Type    | Recursive | Content |
+|------|-------|---------|-----------|---------|
+| 0    | 0x01  | Chunk0  | Yes       | Quest name/description + 0x14 byte info block |
+| 1    | 0x02  | Chunk1  | Yes       | NPC dialog(?) + 0x2C byte info block |
+| 2    | 0x04  | —       | —         | Unknown (no instances found; possibly Chunk2) |
+| 3    | 0x08  | Chunk0  | No        | Episode listing (0x1 prefixed?) |
+| 4    | 0x10  | Chunk1  | No        | JKR-compressed blob, NPC dialog(?) |
+| 5    | 0x20  | Chunk2  | No        | JKR-compressed blob, menu options or quest titles(?) |
+| 6    | 0x40  | —       | —         | Unknown (no instances found) |
+| 7    | 0x80  | —       | —         | Unknown (no instances found) |
+
+### Chunk Types
+
+- **Chunk0**: Contains text data (quest names, descriptions, episode titles) with an accompanying fixed-size info block.
+- **Chunk1**: Contains dialog or narrative text with a larger info block (0x2C bytes).
+- **Chunk2**: Contains menu/selection text.
+
+### Recursive vs Non-Recursive
+
+- **Recursive chunks** (flags 0x01, 0x02): The chunk data itself contains nested sub-chunks that must be parsed recursively.
+- **Non-recursive chunks** (flags 0x08, 0x10, 0x20): The chunk is a flat binary blob. Flags 0x10 and 0x20 are JKR-compressed and must be decompressed before reading.
+
+## Response Format
+
+The server responds with the scenario file data via `doAckBufSucceed`. The response is the raw binary blob matching the requested chunk types. If the scenario file is not found, the server sends `doAckBufFail` to prevent a client crash.
+
+## Current Implementation
+
+Scenario files are loaded from `quests/scenarios/` on disk. The server currently serves them as opaque binary blobs with no parsing. Issue #172 proposes adding JSON/CSV support for easier editing, which would require implementing a parser/serializer for this format.
+
+## JKR Compression
+
+Chunks with flags 0x10 and 0x20 use JPK compression (magic bytes `0x1A524B4A`). See the ReFrontier tool for decompression utilities.