fix(call): bind group streams to relay answer and packetize EAS2 audio

[dryob]

Description

Fix two independent causes of silent or distorted PLANET group audio: registration used locally invented stream IDs instead of the final relay allocation, and CELT group payloads omitted the EAS2 activity bitmap.

• Wait for a successful final PARTICIPATE answer with a media channel and valid AUDIO/VIDEO/DATA source IDs. Register receive IDs from answer field 11 and transmit IDs from field 61; use the allocated AUDIO/DATA IDs on outgoing SRTP. Never fall back to the CC channel or register on a provisional response.
• Correct the existing group-only packetizeNativeGroupOpusPairs() helper: CELT EAS2 activity bitmap after TOC/count and before VBR lengths/data, MSB-first non-silence flags (including unvoiced audio), and correct two-byte VBR sizes.
• Reject unsupported packet layouts instead of silently truncating/dropping them. Update the actual command example with 20 ms paired frames, last-pair silence padding, and explicit per-frame PCM non-silence activity.
• Document the group payload/API contract and add synthetic wire and codec regressions.

This is based directly on main, independent of #241. No incoming-call implementation, auto-join policy, crypto changes, dependency changes, or account/capture artifacts.

Compatibility and limitations

• frameActivity is required for CELT inputs. Only complete pairs of matching mono 20 ms code-0 inputs are supported; invalid layouts throw. SILK/hybrid keep their in-band activity.
• groupDataSessionAfterProvisional remains accepted for source compatibility but is deprecated and ignored.
• EAS2 is group-specific, not standard Opus. Generic codec and 1:1 semantics are unchanged. The example's PCM meter is not the native encoder's VAD.
• This TypeScript port has automated validation only; it has not been exercised in a live LINE call. No live calls or deployment were performed for this PR.

Testing

• Reproduced missing bitmap, wrong long VBR length, unsupported-input acceptance, random registration IDs, rejected/incomplete-answer acceptance, and premature provisional registration on pre-fix behavior; focused tests pass with the fix.
• deno test -A: 357 passed, 7 steps, 0 failed.
• node scripts/test_node_transport.mts: 2 passed.
• deno check example/call/call_on_command.ts: passed.
• deno publish --dry-run --allow-dirty in both packages/linejs and packages/types: passed.
• deno fmt --check for changed TypeScript files and git diff --check: passed.
• Synthetic relay test authenticates/decrypts produced control and AUDIO/DATA SRTP wire, checks stream allocation and timestamp progression. Synthetic PCM tests depacketize EAS2 before stock Opus decoding and compare against separately decoded original frames for CBR/VBR.

Checklist

• Run tests
• Add jsdoc and usage documentation
• Test local automated runtime paths
• Live LINE validation of this TypeScript port