Codex (Civilopedia) Phase 1: data layer — parse Civilopedia.txt and attach pedia keys

[Billytifft]

Summary

Phase 1 (data layer) of the Civilopedia/Codex epic (#997): parse Text/Civilopedia.txt into a queryable model, attach civilopedia keys to all game objects during BIQ/SAV import, and load the text beside PediaIcons during import.

What's included

• C7Engine/C7GameData/Codex.cs — new parser producing Codex (entry dictionary + game-concept keys), CodexEntry, CodexPage.
  • Windows-1252 decoding of the legacy file.
  • #KEY headers → entries; #DESC_<KEY> headers → additional pages; {Title} lines → page titles; ^-prefixed lines → paragraphs (wrapped lines are rejoined).
  • #GAME_CONCEPTS_KEYS → GameConceptKeys list; empty placeholder markers (GAME_CONCEPTS, EOF) are filtered.
  • Inline $LINK<Text=Key> converted to markdown [Text](key:Key); keys are trimmed on lookup (the real file has trailing-space keys like GCON_Enslavement ).
• Keys attached during import for units, buildings, and civilizations (civilopediaEntry on SaveUnitPrototype/UnitPrototype, SaveBuilding/Building, Civilization). Techs/resources/governments/terrain already had them.
• Load pipeline — a new GetCivilopediaTextPath func mirrors the existing GetPediaIconsPath pattern through GameParams, CreateGame, SaveManager.LoadSave, ImportCiv3.ImportSav/Biq, SaveGame.Load, Game.cs, ScenarioSetup, and BuildDevSave.
• Storage — Codex lives on SaveGame / GameData. It is [JsonIgnore] on SaveGame and regenerated from the scenario search path on load, so C7 saves stay portable and text is never duplicated into JSON.
• Tests — EngineTests/GameData/CodexTest.cs (11 tests): parser semantics, Windows-1252, key trimming, game-concept keys, a real-file smoke test against the actual install, and an import integration test (2 Rise of Rome.biq) verifying keys attach and resolve.

Design decisions

1. Legacy Civilopedia.txt parsed as-is, not a native format. Matches the legacy-mode direction and keeps mods working (per issue open question 1). Revisit native prose only if/when standalone content is authored.
2. Naming: Codex* for our feature, Civilopedia kept for legacy artifacts. The new model/API is Codex/CodexEntry/CodexPage; Civilopedia naming remains only where it refers to the Civ3 files/content (Civilopedia.txt, civilopediaEntry keys, path lambdas).
3. Markdown bodies. The parser emits markdown ([Text](key:Key) links, \n\n paragraph breaks, {Title} pages) so Phase 2/3 UI can render with a stock markdown-capable control and the key: links give deep-linking for free.
4. Codex is not part of saves. It is regenerated on load ([JsonIgnore]), resolving issue open question 2: keeps the dictionary on GameData/SaveGame for convenient access, but keeps saves small and language-agnostic.
5. Null-safe for missing keys. Scenario-only objects (e.g. Rise of Rome's PRTO_Fire_Catapult) legitimately have no entry in the installed text. GetEntry returns null rather than throwing; the integration test asserts graceful handling. UI must render a fallback (name + stats) for these.
6. Path resolves to the base ruleset text. Scenarios ship only an override PediaIcons.txt today; there is exactly one Civilopedia.txt in a Complete install, so the path resolves to Conquests/Text/Civilopedia.txt (via the same Util.Civ3MediaPath / scenario-search convention as GetPediaIconsPath), keeping mod override support for any future mod-provided file.

Verified

• dotnet build C7/C7.sln — 0 errors
• dotnet test C7/C7.sln — 83/83 passed (with CIV3_HOME set)
• dotnet format C7/C7.sln whitespace --verify-no-changes — clean

Out of scope (later phases)

UI shell, stat blocks, rendering key: links, deep-linking, and search are Phase 2/3 per #997. Standalone-mode fallback when no text file exists is covered by a Codex warning path (renders empty, callers must handle null).