fix(cli): default blueprint templates to main

[drewstone]

This updates the default blueprint template branch used by cargo tangle blueprint create.

Background

• cli/src/command/create/mod.rs was defaulting to branch = "v2".
• tangle-network/blueprint-template does not have a v2 branch, so blueprint creation can fail.

Changes

• Default template branch to main for all template repos.
• Make docs/setup-service-lifecycle-test.sh robust to templates that specify either branch = "main" or branch = "v2" (it rewrites to local path in both cases).

Verification

• cargo test -p cargo-tangle --tests

[drewstone]

CI rustfmt uses (). I ran and pushed the result (commit ).

[drewstone]

CI rustfmt uses nightly-2025-10-20 (see .github/workflows/ci.yml). I ran cargo +nightly-2025-10-20 fmt --all and pushed the result (commit 97359425).