tooling(chronicle): add a Chronicle append helper with UTC/correction enforcement

[flyingrobots]

Work Type

integrity

Hill Supported

Contributors and agents can append Chronicle entries correctly without hand-rolled shell snippets drifting away from the append-only rules.

Sponsor Actor

• Contributor or agent recording work in the Chronicle
• Maintainer auditing Chronicle history later

Playback

A contributor uses one supported helper to append a Chronicle entry with normalized UTC timestamps and append-only correction support, then the docs point to that helper instead of raw shell fragments.

Problem

Chronicle entry creation still depends on ad hoc shell snippets. That makes timestamp formatting, correction handling, and append-only discipline too easy to get wrong.

Proposed Change

• add a Chronicle append helper
• normalize timestamps to whole-second UTC
• support append-only correction entries
• update Chronicle instructions to point to the helper

Invariants

• Chronicle stays append-only
• helper writes valid JSONL entries
• correction flow adds new entries instead of mutating old ones
• docs stay honest about the supported workflow

Non-Goals

• redesigning the Chronicle format
• introducing remote logging infrastructure
• retroactively rewriting existing Chronicle history

Acceptance / Tests

• helper writes valid Chronicle JSONL entries
• timestamps are normalized to whole-second UTC
• correction entries are supported and documented
• existing Chronicle instructions point to the helper