feat(dashboard): hide token/cost analytics behind config flag (default off) (#25438)

The Analytics page and the token/cost surfaces on the Models page show
local debug estimates only. They count input+output (and a bar viz adds
cache_read+reasoning, missing cache_write entirely) from successful
main-agent responses that returned a usable usage block.

Excluded silently:
- All auxiliary calls — context compression, title generation, vision,
  session search, web extract, smart approvals, MCP routing, plugin LLM
  access (13 production call sites bypass update_token_counts)
- Provider-side retries, fallback attempts
- Any call whose usage block didn't come back
- cache_write_tokens (column exists in sessions table but not returned
  by /api/analytics/models)

Real-world impact: a user on Kimi K2.6 saw 150K local vs 27M on the
OpenRouter side over the same window. Precise-looking numbers next to
provider billing create false confidence and support load.

This change adds dashboard.show_token_analytics (default False) to gate:
- The Analytics nav item (hidden from sidebar when off)
- The Analytics page (renders an explanation card instead of charts)
- Token bars, totals, cost figures, avg/api_calls on the Models page

The Models page keeps capability metadata (context window, vision,
tools, reasoning), the use-as-main/aux menu, sessions count, and
last-used timestamps when the flag is off.

Set dashboard.show_token_analytics: true in config.yaml to opt back in
to the local debug estimate. Fixing the underlying accounting (issue
#23270) is a separate, larger workstream.

Refs: #23270, #21705

hermes_cli/config.py

@@ -971,6 +971,21 @@ DEFAULT_CONFIG = {
     # Web dashboard settings
     "dashboard": {
         "theme": "default",  # Dashboard visual theme: "default", "midnight", "ember", "mono", "cyberpunk", "rose"
+        # Hide the token/cost analytics surfaces (Analytics page, token bars and
+        # cost figures on the Models page) by default.  The numbers shown there
+        # are a local debug estimate: they only count successful main-agent
+        # responses with a usable ``response.usage``, and silently exclude every
+        # auxiliary call (context compression, title generation, vision,
+        # session search, web extract, smart approval, MCP routing, plugin LLM
+        # access) plus provider-side retries, fallback attempts, and any call
+        # whose usage block didn't come back.  Cache writes are also missing
+        # from the API response.  On models with heavy auxiliary traffic
+        # (Kimi K2.6, MiniMax M2.7) the local total can be 10x-100x lower than
+        # the provider bill, which is worse than hiding the numbers entirely
+        # because they look precise enough to compare against the provider.
+        # Set this to True to re-enable the surfaces with the understanding
+        # that the numbers are a local lower-bound estimate, not billing.
+        "show_token_analytics": False,
     },
 
     # Privacy settings