fix(cdk): resolveBedrockModelIds rejects the documented -c string override

[AshrafBen10]

Summary

resolveBedrockModelIds (cdk/src/constructs/bedrock-models.ts) rejects any context value that isn't a real array. But CDK delivers a -c key=value context value as a raw string, not parsed JSON — so the -c form the function's own JSDoc advertises throws at synth:

cdk deploy -c 'bedrockModels=["anthropic.claude-sonnet-4-6"]'
# Error: Context 'bedrockModels' must be a non-empty array of foundation-model IDs …;
#        got "[\"anthropic.claude-sonnet-4-6\"]".

The cdk.context.json array form works; the documented -c CLI form does not.

Context

Flagged by @isadeks in the re-review of #358 as a non-blocking follow-up: the AZ override (resolveAgentCoreAzOverride) was fixed there to JSON.parse a string context value; resolveBedrockModelIds shares the same structural limitation and its JSDoc already documents a -c bedrockModels='[...]' form.

Acceptance criteria

• resolveBedrockModelIds JSON.parses a string context value before the array check, so the -c form and the cdk.context.json array form behave identically.
• A non-JSON / malformed string (a true typo) still fails with the existing clear, key-named error (loud-fail preserved).
• All existing validation still fires (non-array, empty array, non-string/empty entry, region-prefixed us./eu./apac. inference-profile ID).
• Unit tests cover: -c JSON-string array (success), and a JSON string that doesn't parse to an array (throws).
• No new dependencies; tsc, ESLint, and the AI004 masking scan stay clean.

Out of scope

No behavior change to the default model set or the grant sites; this only fixes context-value parsing.

[AshrafBen10]

Starting implementation.

[AshrafBen10]

Fix delivered via PR #358 (commit d1fcec5) rather than a standalone PR, alongside the AZ-override change that prompted it. Will close when #358 merges.