ISSUE-221 - Documentation review - #237

What type of PR is this?

• documentation

What this PR does / why we need it:

Inline docs contradicted schemas, READMEs had broken links. Fix per review comments (@hdamker, @rartych).

• call-handling: single valid POST /sessions example with required offer; drop "add media later" text; pick-up example uses Connected + answer; paths relative to API root.
• registration: PUT refresh algorithm now honours registrationExpireTime (cap/range/min), else TTL_cfg. Min/max clarified as durations relative to request receipt time. Duplicate RFC 3339 line removed.
• events-subscriptions: "three types of events"; subscription examples per deviceId; registration-ends no longer invalidates subscription (matches registration API); fix /sessions/{mediaSessionId} path.
• Blank line after CAMARA:MANDATORY:*:BEGIN markers (Swagger-UI rendering, matches Commonalities template).
• READMEs: remove code/API_definitions/README.MD (root README links YAMLs per release); drop broken API_documentation links; simplify Test_definitions README; update SupportingDocuments index and MeetingMinutes wiki link; stale-doc disclaimer on webrtc voice api.md.

Which issue(s) this PR fixes:

Fixes #221

Special notes for reviewers:

• Just to inform: Current webrtc-call-handling.yaml POST action (create new call) does not support late SDP offer. Current YAML request a mandatory offer. The example was updated according to that.
• Registration expiry: An alignment was required here, so the client-requested value wins within the allowed range (field text from fix: Clarification on registrationExpireTime #165 kept, algorithm aligned to it).
• It was clarified that the subscription survives to an expired registration. So we can keep the simplified relationship that one registration requires a subscription.

Changelog input

 release-note
- fix: Align inline documentation with API definitions and fix README links (webrtc-call-handling, webrtc-registration, webrtc-events-subscriptions)

Additional documentation

n/a