[plugin] Enforce build/deploy architecture consistency (#683)

[sebsto]

Fixes #683

Description of changes

lambda-build and lambda-deploy could independently choose the target architecture, so a user could build an arm64 binary and deploy a function declaring x64 (or the reverse). The deploy "succeeded" but the function was broken at invoke time, with no error at build or deploy.

The OCI PR (#687) introduced the build-manifest.json hand-off but only wired the architecture into the image deploy path. This PR closes the underlying latent bug for the ZIP path and makes a mismatch impossible to deploy silently.

lambda-build

• Adds --architecture <x64|arm64> (default: host).
• The flag actually drives the build: the container is run/pulled/built for that platform (docker --platform linux/<arch>, Apple container --arch <arch>), so the produced binary matches what the manifest records. The CLI-specific spelling lives in each ContainerCLI implementation.
• Both ZIP and OCI backends record the real architecture in build-manifest.json (ZIP previously hardcoded .host).
• A native (Amazon Linux host) build rejects an explicit cross-architecture request, since it can only target the host and would otherwise record a mismatched architecture.

lambda-deploy

• When --architecture is omitted, deploy adopts the architecture recorded in the manifest instead of independently re-defaulting to the host.
• When --architecture is passed and disagrees with the built artifact, deploy fails fast with a descriptive error rather than creating a broken function.
• No manifest (legacy archive output, or --input-directory) falls back to the previous behavior; --architecture remains the way to declare the arch there.

Docs & tests

• Documents the flag and the build→deploy hand-off in the DocC articles.
• Adds unit tests for arg parsing, backend threading, the updated CLI argv, and the deploy-side reconciliation (match / mismatch / omitted / no-manifest).

New/existing dependencies impact assessment, if applicable

No new dependencies.

Conventional Commits

fix: enforce architecture consistency between lambda-build and lambda-deploy

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