Document the reconstructed feature roadmap

ROADMAP.md

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+# Battle for 'Tismo — roadmap
+
+This reconstructs the feature brief that drove the recent work, from the task
+list given in the project chat and the state of the code afterwards. It is a
+reconstruction, not a verbatim copy: where the original wording was lost it has
+been restated from what was actually built.
+
+`[x]` = implemented and covered by the test suite. `[~]` = implemented with a
+simplification worth revisiting. Anything unticked is still open.
+
+## General guidelines
+
+- If an icon is missing, add a dummy SVG that reads `dummy icon - <name>`.
+- Once an item is finished, move on to the next; keep the suite green and add
+  tests for each new pure behaviour.
+- Percentages are for the final figure only; raw effects are stated in the
+  model's own integer units (e.g. popularity points).
+
+## 1. Visual / UI
+
+- [x] City progress bar under the city name, plus a quick production view in
+      the city panel.
+- [x] Remove the city "improve" button; cities improve themselves as railways
+      are laid.
+- [x] Per-improvement buttons above the tile panel, with a control to remove an
+      improvement.
+- [x] Manual unit selection in the stack panel (checklist).
+- [x] Clicking a unit opens the panel for its tile or city.
+- [x] A stack splits immediately when a member leaves it.
+- [x] Logarithmic scale for the population map mode.
+- [x] Building squares drawn around the city icon, in a seeded pattern.
+- [x] Upgrade tooltip forecasts the resulting budget income.
+- [x] Artillery barrages are always visible, dimmed unless selected.
+- [x] Square icon buttons for tile improvements: name in the tooltip, cost
+      beneath the icon.
+- [x] A progress bar for a tile improvement under construction, like a city's.
+- [x] Technology tab: wide, short (3:1) cards in a grid; a focused technology
+      shows a progress bar with `X / Y` to its right; the button no longer
+      repeats the cost.
+- [x] Key art behind the main menu.
+- [x] Double-clicking a city opens its full city panel.
+- [x] Barrages drawn as animated parabolic arcs from attacker to target (SVG
+      Bezier, marching dashes, a shell riding the curve).
+
+## 2. Populations and popularity
+
+- [x] Popularity counted in integer points, shown through a logistic curve
+      (0 -> 50%, +100 -> 75%).
+- [x] Opinions drift one point an hour toward neutral.
+- [x] War effects: declaring war, being declared on (rally when the aggressor is
+      loathed), unit losses and kills, city capture and loss.
+- [x] Pillaging leaves a popularity stain, doubled among the affected peoples.
+- [x] Minorities above 10% cannot be expelled.
+- [~] Structure and city damage is modelled as city population/GDP loss plus
+      improvement hit points, not a dedicated per-structure HP system.
+
+## 3. Nation top info bar
+
+- [x] Month-over-month arrows on population, GDP, GDP per capita, budget and
+      popularity.
+- [x] GDP, population and GDP per capita double their arrow past a 10% move;
+      popularity past ten percentage points.
+- [x] No arrows for January 2000, which has no past month.
+- [x] Popularity tooltip estimates hours/days to neutrality at the drift rate.
+
+## 4. Technologies
+
+- [x] Focused research: every point flows straight into the chosen technology;
+      there is no bank, so no focus means no progress.
+- [x] Committed progress is kept per technology, so changing focus never loses
+      work already done.
+- [x] Repeatable technologies with a 2% cost growth per level, notified without
+      flooding the news list.
+- [x] Theme tabs (Science / Economy / Society / Military).
+- [x] Technology panel shows the research rate rather than a stockpile.
+- [x] Readable effect text for the military and repeatable effects.
+
+## 5. War mechanics
+
+- [x] Zone of control: units deny their tile and the ring around it to hostile
+      movement, mirrored in client prediction; the deliberate goal is exempt so
+      charges resolve.
+- [x] Battleships and ground batteries bombard coastal units and defenceless
+      cities from range.
+- [x] Capturing a city takes the aircraft based there.
+- [x] Infantry capture unaccompanied artillery; a warship over a launch stack
+      sinks it.
+- [x] Trenches: dug by infantry, defensive bonus against melee and artillery,
+      local GDP cost.
+- [x] Combat order: infantry absorbs blows first; exposed support units are hit
+      before dug-in troops.
+- [x] New units: mobile radar (wide vision, captured or destroyed easily) and
+      the launch transport (embark, carry one infantry, disembark a whole
+      stack).
+- [x] Buildable military tile improvements: fortifications (permanent area of
+      control, defensive bonus, battle damage), radar tower (captured by an
+      enemy walking on it), coastal cannon (auto-fires on warships).
+- [x] Embark / disembark orders wired on server and client, with a cargo readout
+      in the unit panel.
+
+## 6. Content and tuning
+
+- [x] Market and Bank base cost reduced tenfold (500k and 1M).
+
+## Open items
+
+- [ ] A dedicated structure hit-point model for cities and tile improvements
+      (see the `[~]` note above).
+- [ ] Real art for the placeholder "dummy icon" SVGs: `icon_radar.svg`,
+      `icon_launch.svg`, `icon_fortifications.svg`, `icon_radar_tower.svg`,
+      `icon_coastal_cannon.svg`, `icon_road.svg`, `icon_railway.svg`.