refactor(shared-tailwind): rewrite themes.css to single-layer shadcn convention

Pre-launch theme system audit found multiple parallel layers in themes.css
(--theme-X full hsl strings, --X partial shadcn aliases, --color-X populated
by runtime store with raw channels) plus dead-code companion files. The
inconsistency caused light-mode regressions when scoped-CSS consumers
wrote `var(--color-X)` standalone — the variable holds raw HSL channels
which is invalid as a color value, browser fell back to inherited (white).

Rewrite to one consistent layer:

  - Source of truth: --color-X defined as raw HSL channels (e.g.
    `0 0% 17%`) in :root, .dark, and all variant [data-theme="..."]
    blocks. Matches the format the runtime store
    (@mana/shared-theme/src/utils.ts) writes, eliminating the
    static-fallback-vs-runtime mismatch and the corresponding flash
    of unstyled content on hydration.

  - @theme inline uses self-reference + Tailwind v4 <alpha-value>
    placeholder so utility classes generate correctly AND opacity
    modifiers work: `text-foreground/50` → `hsl(var(--color-foreground) / 0.5)`.

  - @layer components (.btn-primary, .card, .badge, etc.) wraps
    var(--color-X) refs with hsl() — they were broken in light mode
    too for the same reason.

Convention going forward (also documented in the file header):

  1. Markup: use Tailwind utility classes (text-foreground, bg-card, …)
  2. Scoped CSS: hsl(var(--color-X)) — always wrap with hsl()
  3. NEVER raw var(--color-X) in CSS — that's the bug pattern

Net file: 692 → 580 LOC. Single source layer, no indirection.

Also delete dead companion files (zero imports anywhere):
  - tailwind-v4.css (had broken self-reference, never imported)
  - theme-variables.css (legacy hex-based palette)
  - components.css (legacy component utilities)
  - index.js / preset.js / colors.js (Tailwind v3 preset format,
    irrelevant under Tailwind v4)

package.json exports map shrinks accordingly to just `./themes.css`.

Consumers using `hsl(var(--color-X))` (~379 files across mana-web,
manavoxel-web, arcade-web) keep working unchanged — the public API
name `--color-X` is preserved. Only the broken pattern `var(--color-X)`
(~61 files) needs a follow-up sweep, handled in a separate commit.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/api/src/modules/context/routes.ts

@@ -7,10 +7,11 @@
 
 import { Hono } from 'hono';
 import { consumeCredits, validateCredits } from '@mana/shared-hono/credits';
+import type { AuthVariables } from '@mana/shared-hono';
 
 const LLM_URL = process.env.MANA_LLM_URL || 'http://localhost:3025';
 
-const routes = new Hono();
+const routes = new Hono<{ Variables: AuthVariables }>();
 
 // ─── AI Generation (server-only: mana-llm) ──────────────────