Improve Turkish translation of the landing page

[erenmalkoc]

Improves the Turkish landing page strings in src/i18n/locales/tr.yaml.

• Fix the hero headline and meta description: "olmamak üzere" means "provided that it is not", so the line did not make sense
• Fix the signatory count line, which rendered without a verb ("… kuruluş açık mektubu")
• Update flow_step1 to match the current English source ("About Phone")
• Turn obj_sideloading_q back into a question and fix meaning shifts in obj_security_a, impact_gov_p1, obj_hide_a and precedent_p1
• Use the informal address in the "Fight back" section, like the rest of the page
• Use one Turkish term each for sideloading, the advanced flow and the petition
• Refresh the # [en] comments of the changed keys to the current English source

python lint_yaml.py passes (including the social post length limits) and the site builds.