refactor(frontend): base16 theme contract in a swappable colors.css

Split the palette into two standalone stylesheets:
- colors.css — the 16 base16 slots (--base00..--base0F). This is the
  entire theme swap contract; a generator (e.g. a stylix base16 scheme,
  which is natively base00-base0F) replaces only this file.
- theme.css — the semantic layer (--bg, --purple, …) derived from the
  base16 slots via var()/color-mix. Never changes on a swap.

Every page links colors.css then theme.css; theme.css does NOT @import
colors.css (that would re-bake the slots into it) — they're separate
dist outputs so a swap touches just colors.css. Pixel-identical refactor:
base16 defaults are Catppuccin Mocha and the three off-slot vars
(--crust, --muted, --subtext0) derive via color-mix reproducing their
exact prior hexes.

Wires colors.css through both build.mjs CSS entry lists, the
@hive/shared exports map, and all 7 page templates. css-vars.md + the
frontend.nix output-list comment updated.

frontend/packages/dashboard/build.mjs

@@ -86,11 +86,12 @@ await build({
 });
 
 // Bundle CSS — one entry per page. esbuild resolves @import including
-// the package re-exports from @hive/shared. Each page loads theme.css
-// (the standalone Catppuccin palette — kept its own file so a theme
-// swap replaces only it) + common.css (shared typography, badges,
-// buttons, inbox, side panel) plus its own page-specific bundle.
-for (const entry of ['theme.css', 'common.css', 'dashboard.css', 'flow.css', 'logs.css', 'home.css']) {
+// the package re-exports from @hive/shared. Each page loads colors.css
+// (the standalone base16 palette — the theme swap contract, its own file
+// so a swap replaces only it) + theme.css (the semantic derivation
+// layer) + common.css (shared typography, badges, buttons, inbox, side
+// panel) plus its own page-specific bundle.
+for (const entry of ['colors.css', 'theme.css', 'common.css', 'dashboard.css', 'flow.css', 'logs.css', 'home.css']) {
   await build({
     entryPoints: [src(entry)],
     outfile: staticDir(entry),

frontend/packages/dashboard/src/colors.css

@@ -0,0 +1,6 @@
+/* Standalone base16 palette — re-exports the shared base16 slots so
+   esbuild emits its own `dist/static/colors.css`, linked first by every
+   dashboard page (before theme.css). This is the theme swap contract: a
+   stylix-generated variant replaces only this file. See
+   @hive/shared/colors.css + docs/web-ui/css-vars.md. */
+@import "@hive/shared/colors.css";

frontend/packages/dashboard/src/dashboard.html

@@ -5,6 +5,7 @@
   <meta name="viewport" content="width=device-width, initial-scale=1">
   <title>hyperhive // h1ve-c0re</title>
   <link rel="icon" type="image/svg+xml" href="/favicon.svg">
+  <link rel="stylesheet" href="/static/colors.css">
   <link rel="stylesheet" href="/static/theme.css">
   <link rel="stylesheet" href="/static/common.css">
   <link rel="stylesheet" href="/static/dashboard.css">

frontend/packages/dashboard/src/flow.html

@@ -5,6 +5,7 @@
   <meta name="viewport" content="width=device-width, initial-scale=1">
   <title>hyperhive // FL0W</title>
   <link rel="icon" type="image/svg+xml" href="/favicon.svg">
+  <link rel="stylesheet" href="/static/colors.css">
   <link rel="stylesheet" href="/static/theme.css">
   <link rel="stylesheet" href="/static/common.css">
   <link rel="stylesheet" href="/static/flow.css">

frontend/packages/dashboard/src/index.html

@@ -5,6 +5,7 @@
   <meta name="viewport" content="width=device-width, initial-scale=1">
   <title>hyperhive // h0m3</title>
   <link rel="icon" type="image/svg+xml" href="/favicon.svg">
+  <link rel="stylesheet" href="/static/colors.css">
   <link rel="stylesheet" href="/static/theme.css">
   <link rel="stylesheet" href="/static/common.css">
   <link rel="stylesheet" href="/static/home.css">

frontend/packages/dashboard/src/logs.html

@@ -5,6 +5,7 @@
   <meta name="viewport" content="width=device-width, initial-scale=1">
   <title>hyperhive // LOGS</title>
   <link rel="icon" type="image/svg+xml" href="/favicon.svg">
+  <link rel="stylesheet" href="/static/colors.css">
   <link rel="stylesheet" href="/static/theme.css">
   <link rel="stylesheet" href="/static/common.css">
   <link rel="stylesheet" href="/static/logs.css">

frontend/packages/dashboard/src/theme.css

@@ -1,6 +1,6 @@
-/* Standalone theme bundle — re-exports the shared Catppuccin palette so
-   esbuild emits it as its own `dist/static/theme.css`, linked first by
-   every dashboard page. Kept separate from the page bundles so a theme
-   swap (e.g. stylix) replaces only this file. See @hive/shared/theme.css
-   + docs/web-ui/css-vars.md. */
+/* Standalone semantic theme layer — re-exports the shared derivation so
+   esbuild emits it as its own `dist/static/theme.css`, linked by every
+   dashboard page right after colors.css. The base16 slots it derives
+   from live in colors.css (the swap contract); a theme swap replaces
+   only that file. See @hive/shared/theme.css + docs/web-ui/css-vars.md. */
 @import "@hive/shared/theme.css";