Add replica count support to tvc deploy create

[emostov]

What

tvc deploy create now supports specifying a desired replica count, defaulting to 1:

• --replicas <N> flag / TVC_REPLICAS env var, overriding the config file like the other flags
• replicas field in the deploy config file; tvc deploy init templates include "replicas": 1
• The create intent always sends an explicit replica count (previously omitted, leaving it to the server default)
• A count of 0 is rejected client-side with a clear validation error

Notes

• Config files written before the replicas field existed keep working (serde default of 1).
• Seeding a config from an existing deployment defaults to 1 replica since the fetched deployment doesn't carry its desired replica count.

Testing

• cargo test (all suites pass), cargo clippy --all-targets --all-features -D warnings clean.
• New tests: replicas default, flag-overrides-file, zero rejection, intent wiring, backward-compat deserialization.

🤖 Generated with Claude Code

[daniilrrr]

approved with nits