fix(ssh): reject control characters in ssh_add_host_key inputs

[jayantkamble10000]

What

The ssh_add_host_key action builds a known_hosts line from the host, key_type, and key fields and writes it to the line-oriented known_hosts file. The host, key, and key_type fields on AddHostKeySchema are only length-validated, so a value containing a newline can write more than one line into known_hosts.

Why

known_hosts is line-oriented; an embedded newline in any of these fields breaks the one-entry-per-line invariant and lets a single call add extra entries. Rejecting control characters keeps each call to a single, well-formed entry.

Change

python/coinbase-agentkit/coinbase_agentkit/action_providers/ssh/schemas.py — add a field_validator on host, key, and key_type in AddHostKeySchema that rejects ASCII control characters (newline, CR, NUL, etc.).

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 0 Sum 1