refactor: remove direct Vaultwarden fallback

[bglusman]

Summary

• remove the direct Vaultwarden REST fallback from secrets-client
• rename the read path from vault to resolver and keep resolution to env -> fnox
• update docs, install/doctor messaging, and tests to stop advertising direct Vaultwarden support
• make a credential injection test independent of ambient provider env vars

Vaultwarden can still be used behind fnox as an operator-chosen storage backend; Calciforge no longer calls Vaultwarden APIs or reads SECRETS_VAULT_* directly.

Verification

• PATH="/Users/80260986/.rustup/toolchains/stable-aarch64-apple-darwin/bin:/Users/80260986/.codex/tmp/arg0/codex-arg0661YYe:/Users/80260986/.bun/bin:/Users/80260986/.antigravity/antigravity/bin:/Users/80260986/.opencode/bin:/Applications/Postgres.app/Contents/Versions/latest/bin:/Users/80260986/.codeium/windsurf/bin:/Applications/gg.app/Contents/MacOS/:/opt/homebrew/opt/node@14/bin:/Users/brianglusman/.erlangInstaller/23.0.2/bin:/Users/80260986/.asdf/shims:/opt/homebrew/opt/asdf/libexec/bin:/Users/80260986/bin:./bin:/Users/80260986/.duckdb/cli/latest:/Users/80260986/.asdf/installs/nodejs/25.1.0/bin/:/Users/80260986/.local/bin:/Applications/Visual\ Studio\ Code.app/Contents/Resources/app/bin:/opt/homebrew/bin/:/Applications/SnowSQL.app/Contents/MacOS:/opt/homebrew/bin:/opt/homebrew/sbin:/usr/local/bin:/System/Cryptexes/App/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/local/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/appleinternal/bin:/opt/pmk/env/global/bin:/Library/TeX/texbin:/Users/80260986/.cargo/bin:/bin:/Applications/Codex.app/Contents/Resources" RUSTC="/Users/80260986/.rustup/toolchains/stable-aarch64-apple-darwin/bin/rustc" RUSTDOC="/Users/80260986/.rustup/toolchains/stable-aarch64-apple-darwin/bin/rustdoc" "/Users/80260986/.rustup/toolchains/stable-aarch64-apple-darwin/bin/cargo" fmt --all -- --check
• PATH="/Users/80260986/.rustup/toolchains/stable-aarch64-apple-darwin/bin:/Users/80260986/.codex/tmp/arg0/codex-arg0661YYe:/Users/80260986/.bun/bin:/Users/80260986/.antigravity/antigravity/bin:/Users/80260986/.opencode/bin:/Applications/Postgres.app/Contents/Versions/latest/bin:/Users/80260986/.codeium/windsurf/bin:/Applications/gg.app/Contents/MacOS/:/opt/homebrew/opt/node@14/bin:/Users/brianglusman/.erlangInstaller/23.0.2/bin:/Users/80260986/.asdf/shims:/opt/homebrew/opt/asdf/libexec/bin:/Users/80260986/bin:./bin:/Users/80260986/.duckdb/cli/latest:/Users/80260986/.asdf/installs/nodejs/25.1.0/bin/:/Users/80260986/.local/bin:/Applications/Visual\ Studio\ Code.app/Contents/Resources/app/bin:/opt/homebrew/bin/:/Applications/SnowSQL.app/Contents/MacOS:/opt/homebrew/bin:/opt/homebrew/sbin:/usr/local/bin:/System/Cryptexes/App/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/local/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/appleinternal/bin:/opt/pmk/env/global/bin:/Library/TeX/texbin:/Users/80260986/.cargo/bin:/bin:/Applications/Codex.app/Contents/Resources" RUSTC="/Users/80260986/.rustup/toolchains/stable-aarch64-apple-darwin/bin/rustc" RUSTDOC="/Users/80260986/.rustup/toolchains/stable-aarch64-apple-darwin/bin/rustdoc" "/Users/80260986/.rustup/toolchains/stable-aarch64-apple-darwin/bin/cargo" test -p secrets-client
• PATH="/Users/80260986/.rustup/toolchains/stable-aarch64-apple-darwin/bin:/Users/80260986/.codex/tmp/arg0/codex-arg0661YYe:/Users/80260986/.bun/bin:/Users/80260986/.antigravity/antigravity/bin:/Users/80260986/.opencode/bin:/Applications/Postgres.app/Contents/Versions/latest/bin:/Users/80260986/.codeium/windsurf/bin:/Applications/gg.app/Contents/MacOS/:/opt/homebrew/opt/node@14/bin:/Users/brianglusman/.erlangInstaller/23.0.2/bin:/Users/80260986/.asdf/shims:/opt/homebrew/opt/asdf/libexec/bin:/Users/80260986/bin:./bin:/Users/80260986/.duckdb/cli/latest:/Users/80260986/.asdf/installs/nodejs/25.1.0/bin/:/Users/80260986/.local/bin:/Applications/Visual\ Studio\ Code.app/Contents/Resources/app/bin:/opt/homebrew/bin/:/Applications/SnowSQL.app/Contents/MacOS:/opt/homebrew/bin:/opt/homebrew/sbin:/usr/local/bin:/System/Cryptexes/App/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/local/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/appleinternal/bin:/opt/pmk/env/global/bin:/Library/TeX/texbin:/Users/80260986/.cargo/bin:/bin:/Applications/Codex.app/Contents/Resources" RUSTC="/Users/80260986/.rustup/toolchains/stable-aarch64-apple-darwin/bin/rustc" RUSTDOC="/Users/80260986/.rustup/toolchains/stable-aarch64-apple-darwin/bin/rustdoc" "/Users/80260986/.rustup/toolchains/stable-aarch64-apple-darwin/bin/cargo" test -p security-proxy credentials

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