feat(error): bounded application error context facade

[zackees]

Goal

Allow consumer applications to replace direct anyhow use with a kernal-api-owned, bounded error context type while preserving fail-loud diagnostics.

Consumer

zackees/fastled-wasm currently uses anyhow::{Result, Context, bail} across archive, install, build, project, cache, runtime, and viewer business logic. Clap and serde have already been removed from that application in favor of kernal-api facades.

Acceptance criteria

• Public opt-in error-context feature that does not pull application-specific dependencies.
• Owned Error type supporting static/dynamic messages, Display, std::error::Error, and source chaining for standard errors.
• Result<T> alias plus ergonomic context and construction helpers sufficient for the FastLED migration.
• Bounded formatting / no accidental input echo policy documented and covered by contract tests.
• FastLED can remove its direct anyhow manifest dependency and preserve its existing user-facing error context.

Refs #215.

[zackees]

Complete and adopted on both sides; closing with the evidence rather than leaving it open.

kernal-api — gated behind error-context, implemented in src/error.rs.. It landed with #220's application-foundations rebase.

FastLED — adopted through the pinned release tag: crates/fastled-cli/src/error_compat.rs: pub(crate) use kernal_api::error::{message, Context, Error, Result};

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