feat(web): public /join/[token] page + https invite url

Clickable HTTPS invite URLs replace the raw ic://join/<token> as the
primary share format. Someone receiving a link in Slack now lands on
a friendly page with install instructions, not a dead-end.

Backend:
- createMyInvite returns a new joinUrl field
  (https://claudemesh.com/join/<token>) alongside the existing
  ic://join/<token> inviteLink and raw token. Schema + Hono route
  updated. ic:// scheme stays — CLI parses both.
- New GET /api/public/invite/:token in packages/api/src/modules/public/
  (unauthed). Decodes the base64url payload, verifies ed25519
  signature against owner_pubkey using the same canonicalInvite()
  contract the broker enforces on join, then joins mesh/invite/user
  to return the shape needed by the landing page. Does NOT mutate
  usedCount — this is a read-only preview.
- Error taxonomy: malformed | bad_signature | expired | revoked |
  exhausted | mesh_archived | not_found. Each returned with any
  metadata we CAN surface (meshName, inviterName, expiresAt) so the
  error page can be specific ("ask Jordan for a new one").
- cache-control: public max-age=30 on valid invites, no-store on
  errors (reasons flip as state changes).

Frontend:
- New public route /[locale]/join/[token] (no auth). Server
  Component fetches the preview endpoint, branches on valid/invalid,
  renders a minimal landing-design-language shell (wordmark header,
  clay accents, serif headlines, mono commands).
- Valid-invite view: "You're invited to {meshName}", inviter +
  role + member-count lede, install-toggle component.
- Invalid-invite view: per-reason error copy + inviter name when
  available + link back to /.
- InstallToggle client component: three-way state
  (unknown/yes/no). Asks "first time / already set up?", then shows
  either the 3-step install+init+join path with per-step copy
  buttons, or the single claudemesh join <token> command for users
  who have the CLI. Every code block has copy-to-clipboard.
- Security footer: "ed25519 keypair generated locally, you keep
  your keys, broker sees ciphertext only, leave anytime with
  claudemesh leave <mesh-slug>".

Invite generator (/dashboard/meshes/[id]/invite):
- QR code now encodes the HTTPS joinUrl instead of ic:// (phone
  cameras land on the web page → friendly path).
- Primary CTA copies the HTTPS URL. Secondary "Copy CLI command"
  for fast-path users. Footer explanation updated.

CLI coordination note: dispatched to broker/db lane — claudemesh CLI
needs to accept BOTH ic://join/<token> AND
https://claudemesh.com/join/<token> (extract <token> from pathname).
Server side already returns both.

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

packages/api/src/modules/mesh/mutations.ts

@@ -10,6 +10,7 @@ import type {
 } from "../../schema";
 
 const BROKER_URL = process.env.NEXT_PUBLIC_BROKER_URL ?? "ws://localhost:7900";
+const APP_URL = process.env.NEXT_PUBLIC_URL ?? "https://claudemesh.com";
 
 /**
  * Canonical invite bytes — MUST match the broker's canonicalInvite()
@@ -236,5 +237,6 @@ export const createMyInvite = async ({
     token: created!.token,
     expiresAt: created!.expiresAt,
     inviteLink: `ic://join/${token}`,
+    joinUrl: `${APP_URL.replace(/\/$/, "")}/join/${token}`,
   };
 };