feat: Start sessions immediately when transcribing is enabled

[bgrozev]

When enableTranscription is true, bypass the min-participants threshold so Jingle/Colibri sessions start with a single participant.

Two changes in JitsiMeetConferenceImpl:

• checkMinParticipants(): set minParticipants = 1 when transcription is enabled
• setEnableTranscribing(true): if members are already in the room but sessions have not started yet (participants empty), trigger invitations immediately

Also extracts inviteAllChatMembers() to avoid code duplication between the two callsites.

[codecov]

Codecov Report

❌ Patch coverage is 26.31579% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 26.36%. Comparing base (8e8c9d2) to head (501ca61).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
...tsi/jicofo/conference/JitsiMeetConferenceImpl.java	26.31%	12 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1281      +/-   ##
============================================
- Coverage     26.38%   26.36%   -0.03%     
- Complexity      474      475       +1     
============================================
  Files           126      126              
  Lines          7861     7871      +10     
  Branches       1213     1215       +2     
============================================
+ Hits           2074     2075       +1     
- Misses         5478     5486       +8     
- Partials        309      310       +1     

Files with missing lines	Coverage Δ
...tsi/jicofo/conference/JitsiMeetConferenceImpl.java	38.43% <26.31%> (-0.29%)	⬇️

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