docs(kas bridge): add basic model

[danwt]

Description

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Closes #XXX

All items are required. Please add a note to the item if the item is not applicable and
please add links to any relevant follow-up issues.

PR review checkboxes:

I have...

• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md
• Targeted PR against the correct branch
• included the correct type prefix in the PR title
• Linked to the GitHub issue with discussion and accepted design
• Targets only one GitHub issue
• Wrote unit and integration tests
• Wrote relevant migration scripts if necessary
• All CI checks have passed
• Added relevant godoc comments
• Updated the scripts for local run, e.g genesis_config_commands.sh if the PR changes parameters
• Add an issue in the e2e-tests repo if necessary

SDK Checklist

• Import/Export Genesis
• Registered Invariants
• Registered Events
• Updated openapi.yaml
• No usage of go map
• No usage of time.Now()
• Used fixed point arithmetic and not float arithmetic
• Avoid panicking in Begin/End block as much as possible
• No unexpected math Overflow
• Used sendCoin and not SendCoins
• Out-of-block compute is bounded
• No serialized ID at the end of store keys
• UInt to byte conversion should use BigEndian

Full security checklist here

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For Reviewer:

• Confirmed the correct type prefix in the PR title
• Reviewers assigned
• Confirmed all author checklist items have been addressed

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After reviewer approval:

• In case the PR targets the main branch, PR should not be squash merge in order to keep meaningful git history.
• In case the PR targets a release branch, PR must be rebased.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 22.02%. Comparing base (0fdd5de) to head (490dc36).
Report is 63 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1882      +/-   ##
==========================================
- Coverage   22.54%   22.02%   -0.53%     
==========================================
  Files         591      601      +10     
  Lines      129993   141737   +11744     
==========================================
+ Hits        29309    31219    +1910     
- Misses      96797   105761    +8964     
- Partials     3887     4757     +870     

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