fix(security): replace SecretString with String for API response tokens

[spetz]

SDK consumers had to depend on the secrecy crate just to read
token values returned from create-PAT and login endpoints.
These are API response fields intentionally exposed to the
caller over the wire — wrapping them in SecretString added
friction (custom Debug impls, serialize_secret annotations,
expose_secret() calls) without meaningful security benefit.

Changes RawPersonalAccessToken.token and TokenInfo.token from
SecretString to plain String. Leaves SecretString in place for
actual secrets: user passwords, credentials, and PAT values
used in login commands.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.13%. Comparing base (601e597) to head (e4d264a).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3008      +/-   ##
============================================
- Coverage     72.18%   72.13%   -0.06%     
  Complexity      930      930              
============================================
  Files          1122     1120       -2     
  Lines         93502    93489      -13     
  Branches      70851    70849       -2     
============================================
- Hits          67494    67437      -57     
- Misses        23441    23461      +20     
- Partials       2567     2591      +24     

Components	Coverage Δ
Rust Core	72.87% <100.00%> (-0.07%)	⬇️
Java SDK	62.08% <ø> (ø)
C# SDK	67.43% <ø> (-0.21%)	⬇️
Python SDK	81.43% <ø> (ø)
Node SDK	91.53% <ø> (+0.12%)	⬆️
Go SDK	38.68% <ø> (ø)

Files with missing lines	Coverage Δ
...onal_access_tokens/create_personal_access_token.rs	88.88% <ø> (ø)
core/cli/src/commands/binary_system/login.rs	50.00% <ø> (ø)
core/common/src/traits/binary_mapper.rs	79.34% <100.00%> (-0.06%)	⬇️
core/sdk/src/http/http_client.rs	91.45% <ø> (ø)
core/server/src/http/mapper.rs	85.24% <100.00%> (ø)
core/server/src/http/personal_access_tokens.rs	87.23% <ø> (ø)

... and 31 files with indirect coverage changes

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