Refine large map viewport controls

docs/ARCHITECTURE.md

@@ -61,4 +61,6 @@ Inventory and campaign flags are copied from `CampaignState` into `BattleState`
 
 The battle scene owns presentation feedback: briefing and result states use menu BGM, briefing headers combine `CampaignState` chapter ranges, campaign order, and title data with `BattleState` briefing, objective text, condition-progress text, and defeat-risk text, active battles use battle BGM and show an objective/progress/risk panel fed by `BattleState`, objective-update signals show a short HUD notice and refresh the objective panel immediately, dialogue lines can show optional cached portrait textures or speaker-initial fallback panels in an expanded visual-novel-style panel, can place the portrait on the left or right side of that panel, and expose progress plus previous-line controls while a sequence is open, the side HUD reuses cached officer portrait textures or class sprites for the selected unit or hovered unit and formats focus text with role, movement type, current terrain move cost, defense/avoid bonuses, core stats, status effects, and gear, board maps can draw a scenario background texture under translucent terrain overlays, connected road segments, terrain detail patterns, and shoreline/castle/forest/hill edge blends, board units render class sprite tokens or generic-enemy transparent class cutouts, team rings, class badges, generic-enemy marks, officer pins, low-HP warning rings, HP bar color states, and active support/debuff/poison/seal/snare/disarm status pips from battle state fields, item buttons can show optional cached item icons, hover previews are rendered as target badges from existing `BattleState` forecast APIs, equipment option menus show stat/range/effect deltas, result and inventory summaries show named equipment with compact rarity tags, selected area tactics highlight their affected cells, the Threat toggle overlays enemy physical and hostile tactic reach while tile info names threat sources, estimates physical damage, and summarizes hostile tactic damage or status effects against occupied cells, log/result hooks trigger placeholder SFX, support, debuff, poison, seal, snare, disarm, objective updates, AI target-focus changes, and item/gold pickup effects use distinct feedback, `BattleState.unit_motion_requested` asks the scene to interpolate a unit's draw position during movement, `BattleState.unit_action_motion_requested` keeps its rules-facing signal shape while the scene maps attacker class ids to infantry, archer, cavalry, command, and heavy attack presentation profiles, and `BattleState.combat_feedback_requested` asks the scene to draw transient floating combat text without changing battle rules.
 
+Large tactical maps are presented through a fixed visible map window rather than by shrinking the whole board. `BattleScene` keeps a clamped `board_scroll_offset`, scrolls the board while the mouse is near or slightly outside the visible map edge, ignores board clicks outside the visible map window, and draws a small minimap plate inside the map view; clicking or dragging the minimap recenters the tactical viewport, while action feedback can focus the board on off-screen cells before motion or combat effects play.
+
 The `New Campaign` button clears `user://campaign_save.json`, resets campaign state to the first scenario, and reloads the opening briefing.