fix(ssh-console): handle silent Lenovo SOL activation

[williampnvidia]

Lenovo XCC3 can split a failed SOL activation response across multiple SSH
packets. The current implementation can see the initial error text, satisfy its
byte-count check, and declare activation successful before the trailing
system> prompt arrives.

The SR650 V4 fallback has the opposite problem: a successful console start
can transition into SOL without emitting any response. Waiting for positive
output therefore times out even though the console is active.

This change:

• stops accepting Lenovo activation based only on received byte count
• evaluates output after the final command in each Lenovo activation sequence
• treats a returned system> prompt as activation failure
• accepts a silent activation after a short response grace period
• preserves the legacy Lenovo command sequence and SR650 V4 fallback
• leaves activation handling for other BMC vendors unchanged
• updates the SSH mock to reproduce fragmented XCC3 failure output and silent
  console start success

Related issues

Follow-up to #2919 and #2943.

Related to #5173, but this does not address the separate XCC firmware condition
where an SOL channel remains stuck in In Progress.

Type of Change

• Add - New feature or capability
• Change - Changes in existing functionality
• Fix - Bug fixes
• Remove - Removed features or deprecated functionality
• Internal - Internal changes (refactoring, tests, docs, etc.)

Breaking Changes

• This PR contains breaking changes

Testing

• Unit tests added/updated
• Integration tests added/updated
• Manual testing performed
• No testing required (docs, internal refactor, etc.)

Validation will include:

• cargo +nightly-2026-06-16 fmt --all -- --check
• focused Lenovo fallback integration testing
• the complete carbide-ssh-console test suite
• cargo clippy -p carbide-ssh-console --all-targets -- -D warnings
• cargo make --no-workspace clippy-flow

Additional Notes

The same behavior was backported to the exact deployed v2.0.2 source and tested
using the pinned v2.0.2 Linux build container. Its focused Lenovo integration
test, SSH-console integration suite, formatting, clippy, full-workspace release
build, and production-runtime image checks passed.

Live Lenovo XCC3 validation has not yet been performed with the patched image.

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