feat(photon): upgrade to spectrum-ts 3.0.0 (pinned) with markdown + reactions

Pin spectrum-ts to exactly 3.0.0 (was ^1.18.0 plus an `npm install
spectrum-ts@latest` on every setup) so breaking SDK majors can't take
down fresh installs silently; `hermes photon setup` now runs `npm ci`.
Upgrade procedure documented in the README.

Migrate resolveSpace to the v3 namespace API: `im.space.create(phone)`
for DMs and `im.space.get(id)` for everything else — group spaces are
now rehydratable from their persisted id after a sidecar restart, which
v1 could not do.

Markdown: replies go out via the v3 `markdown()` builder (iMessage
renders natively; other Spectrum platforms degrade to plain text).
`PHOTON_MARKDOWN=false` reverts to the stripped plain-text path.

Reactions, behind PHOTON_REACTIONS (default off): lifecycle tapbacks
(👀 while processing, 👍/👎 on completion) via new sidecar /react and
/unreact endpoints with per-target reaction-handle tracking, and user
tapbacks on bot-sent messages routed to the agent as synthetic
`reaction:added:<emoji>` events.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

plugins/platforms/photon/plugin.yaml

@@ -1,7 +1,7 @@
 name: photon-platform
 label: iMessage via Photon
 kind: platform
-version: 0.2.0
+version: 0.3.0
 description: >
   Photon Spectrum gateway adapter for Hermes Agent.
   Connects to iMessage (and other Spectrum interfaces) through Photon's
@@ -78,3 +78,11 @@ optional_env:
     description: "Enable Spectrum SDK telemetry in the sidecar (true/false, default false; toggle with `hermes photon telemetry on|off`)"
     prompt: "Enable Spectrum telemetry? (true/false)"
     password: false
+  - name: PHOTON_MARKDOWN
+    description: "Send agent replies as markdown — iMessage renders it natively, other Spectrum platforms degrade to plain text (true/false, default true)"
+    prompt: "Render replies as markdown? (true/false)"
+    password: false
+  - name: PHOTON_REACTIONS
+    description: "Tapback 👀/👍/👎 on messages as processing status and route tapbacks on bot messages to the agent (true/false, default false)"
+    prompt: "Enable reaction tapbacks? (true/false)"
+    password: false