add -hrv parameters to fetch HRV data

[eskimokk]

fetch hrv data from web-api:
https://dev.fitbit.com/build/reference/web-api/heartrate-variability/

[Copilot]

Pull request overview

Adds HRV (Heart Rate Variability) support to fitbit-cli, enabling users to fetch and display HRV summary data from the Fitbit Web API in table, JSON, and raw-JSON output modes.

Changes:

• Introduces a new --hrv [DATE[,DATE]|RELATIVE] CLI flag wired through all output modes.
• Adds Fitbit API client support for HRV summary fetching.
• Adds an HRV formatter and CLI parsing tests, plus accompanying design/plan docs.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tests/cli_test.py	Adds parsing tests covering --hrv alone, with JSON/raw-JSON, and with several date formats.
fitbit_cli/output.py	Plumbs args.hrv into table_display, json_display, and raw_json_display.
fitbit_cli/formatter.py	Adds display_hrv() to render HRV data as a rich table or snake_case JSON structure.
fitbit_cli/fitbit_api.py	Adds get_hrv_summary() (and an intraday variant) to call the HRV endpoint(s).
fitbit_cli/cli.py	Adds the --hrv flag using the shared parse_date_range mechanism and default-to-today behavior.
docs/superpowers/specs/2026-03-31-hrv-support-design.md	Design doc describing endpoints, response shape, and implementation approach.
docs/superpowers/plans/2026-03-31-hrv-support.md	Step-by-step implementation plan for adding HRV support.

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[veerendra2]

Hi @eskimokk, thanks for the PR. One small request — could you please remove the docs/superpowers/ directory (plans/ and specs/ files) from this PR? as those are AI agent planning artifacts and not required be included in the repository.

Meanwhile, I will create another PR to fix the Pytest pipline

EDIT

• Fix CI #30

[veerendra2]

Tested locally. LGTM

[veerendra2]

@eskimokk Feel free to merge, when are you ready

[eskimokk]

@eskimokk Feel free to merge, when are you ready

please merge