Diet has a big effect on mental health, but any one given food usually won't create a big difference. Lithium is definitely very beneficial for people with bipolar disorder, but the amount of bioavailable lithium in food is usually pretty low. It's really hard to know just how much of a certain substance you're getting when it's solely by diet; it's much more measurable and replicable when you're taking an exact, concentrated dose of something on a consistent schedule. When you're eating food, you just can't reliably know what you're getting, and how much.

It's certainly possible you found some food with particularly high concentrations of bioavailable lithium and then consumed enough of it to have an effect, but unless you were tracking it pretty closely or were into some really unusual foods, my guess is your overall lithium absorption probably didn't increase much.

Regarding lithium and salt: lithium does have a relationship with sodium and there can be a higher requirement for sodium when you take lithium, but this is typically only ever going to be relevant for people who are prescribed lithium medication or are consuming an unusually high level of lithium in their food.

It's the same thing with stuff like curcumin. Curcumin (one of the components of turmeric) definitely reduces inflammation, but eating food with turmeric once per day is probably only going to have a tiny marginal effect, even after a year. But consuming curcumin (ideally theracurmin) in capsule form could have an effect within hours or days, and you can judge exactly what it is and isn't doing for you.

These things are important for averages; if people in a certain culture eat 500x more turmeric on average over their lifetime than another culture, then on average their rates of inflammation may be lower. But a random person saying "I want to reduce my inflammation" probably should try the pills first.

Same with lithium in water supplies. It's an cumulative thing that can affect a population over generations, but the concentration is usually too low to drink tap water with lithium in it for a month and actually notice changes.

Trying to treat serious psychological symptoms with rough approximations of potentially biounavailable versions of substances in food that you consume in inconsistent quantities and at inconsistent intervals really isn't a scientific way to address issues. I think if you want to see if vitamin C might help you with something, you should just take vitamin C supplements for a few weeks or months (at the same dose and roughly the same time every day). Same with lithium or anything else (though lithium treatment probably shouldn't be undergone without a doctor and a prescription). This can be complicated because sometimes substances work differently or more effectively when taken with other things that modulate or potentiate them (like coffee vs. caffeine pills), so sometimes consuming food or consuming multiple substances that mimic the ratios found in food can give a better outcome. But in general, I think diet is just too blunt an instrument for this kind of thing.

And I'd go even further and say that concentrated rosemary/sage oil and vitamin C supplements probably aren't going to help most people (unless they were already deficient in vitamin C, which is pretty rare in developed countries) in general. Of the things you listed, lithium is the only substance I think would have a significant effect. If you really did consume more lithium from the change in diet (though I still think it's unlikely for you to know if you actually did or didn't consume significantly more bioavailable lithium), it's plausible all of your symptom changes could be explained by that. Lithium has been shown to reduce mood swings (including anger), anxiety, and suicidal thoughts.

I would say one of the most significant effects of diet on physical and mental health (once you're already getting the right nutrients) is from avoiding foods which may cause immune responses like allergic reactions and inflammation. If your diet change resulted in you eating less of certain other foods, it's plausible that it was those foods that were partially contributing to your symptoms.