feat(capabilities): Merge byoc capabilities with existing capabilities and pricing

[eliteprox]

What does this pull request do? Explain your changes. (required)

Merges BYOC external capability pricing into the existing OrchestratorInfo.CapabilitiesPrices response, making BYOC capabilities discoverable through the same gRPC channel used for built-in capabilities like Live Video to Video. This eliminates the need for clients to call a separate HTTP endpoint to discover which BYOC capabilities an orchestrator offers and at what price.

A new Capability_BYOC (37) enum value is used as the capability ID, with the registered BYOC capability name (e.g., "comfystream") placed in the PriceInfo.Constraint field — the same pattern used by LV2V models (capability 35 + constraint = model_id).

Specific updates (required)

• Added Capability_BYOC = 37 to the capability enum in core/capabilities.go and registered "byoc" in CapabilityNameLookup
• Enhanced GetCapabilitiesPrices in core/orchestrator.go to iterate over registered external capabilities (ExternalCapabilities.Capabilities) and append a PriceInfo entry for each, using Capability_BYOC as the capability ID and the capability name as the constraint
• Price resolution follows the existing pattern: looks up per-sender pricing first, falls back to the "default" price, and skips capabilities with no valid price

How did you test each of these updates (required)

• Tested against the companion Python gateway client (livepeer-python-gateway) which parses capabilities_prices entries with capability 37 to discover BYOC capabilities and construct payment tickets using the same _select_price_info path as LV2V

Does this pull request close any open issues?

No

Checklist:

• Read the contribution guide
• make runs successfully
• All tests in ./test.sh pass
• README and other documentation updated
• Pending changelog updated

[codecov]

Codecov Report

❌ Patch coverage is 70.58824% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 32.51619%. Comparing base (f117b44) to head (e386a7b).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
core/orchestrator.go	70.58824%	3 Missing and 2 partials ⚠️

Additional details and impacted files

@@                 Coverage Diff                 @@
##              master       #3871         +/-   ##
===================================================
+ Coverage   32.47906%   32.51619%   +0.03713%     
===================================================
  Files            170         170                 
  Lines          41673       41690         +17     
===================================================
+ Hits           13535       13556         +21     
+ Misses         27113       27111          -2     
+ Partials        1025        1023          -2     

Files with missing lines	Coverage Δ
core/capabilities.go	81.57895% <ø> (ø)
core/orchestrator.go	72.70115% <70.58824%> (-0.05290%)	⬇️

... and 5 files with indirect coverage changes

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Files with missing lines	Coverage Δ
core/capabilities.go	81.57895% <ø> (ø)
core/orchestrator.go	72.70115% <70.58824%> (-0.05290%)	⬇️

... and 5 files with indirect coverage changes

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