feat(cli): add context show and session status commands

[atharvalade]

Which issue does this PR close?

Closes #3000

Rationale

The CLI lacked observability into context configuration and login session state, forcing users to manually read ~/.iggy/contexts.toml or run authenticated commands to check connectivity.

What changed?

Previously there was no way to inspect what a context contains or whether a login session is active without workarounds. Users had to read raw TOML files or run iggy me and hope it worked.

This adds iggy context show <name> to display a named context's full configuration (transport, addresses, TLS, credentials with masking) and iggy session status to check the local keyring for an active login session and show which server it targets — both without requiring a server connection.

Local Execution

• Passed
• Pre-commit hooks ran

AI Usage

1. Opus 4.6
2. Minimal AI used
3. Yes all code can be explained

[codecov]

Codecov Report

❌ Patch coverage is 47.94521% with 38 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.69%. Comparing base (27f0f11) to head (f148605).

Files with missing lines	Patch %	Lines
...re/cli/src/commands/binary_context/show_context.rs	66.00%	4 Missing and 13 partials ⚠️
...e/cli/src/commands/binary_system/session_status.rs	0.00%	16 Missing ⚠️
core/cli/src/main.rs	28.57%	5 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3096      +/-   ##
============================================
- Coverage     72.71%   72.69%   -0.02%     
  Complexity      943      943              
============================================
  Files          1117     1119       +2     
  Lines         96285    96358      +73     
  Branches      73485    73558      +73     
============================================
+ Hits          70014    70050      +36     
- Misses        23725    23746      +21     
- Partials       2546     2562      +16     

Components	Coverage Δ
Rust Core	73.43% <47.94%> (-0.03%)	⬇️
Java SDK	62.30% <ø> (ø)
C# SDK	69.40% <ø> (ø)
Python SDK	81.43% <ø> (ø)
Node SDK	91.53% <ø> (ø)
Go SDK	38.97% <ø> (ø)

Files with missing lines	Coverage Δ
core/cli/src/args/context.rs	100.00% <ø> (ø)
core/cli/src/args/mod.rs	78.57% <ø> (ø)
core/cli/src/main.rs	90.97% <28.57%> (-1.25%)	⬇️
...e/cli/src/commands/binary_system/session_status.rs	0.00% <0.00%> (ø)
...re/cli/src/commands/binary_context/show_context.rs	66.00% <66.00%> (ø)

... and 9 files with indirect coverage changes

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